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<div class="chapter" title="Chapter 11. System Management">
<div class="titlepage">
<div>
<div>
<h2 class="title">
<a name="management-chapt"></a>Chapter 11. System Management</h2>
</div>
<div>
<div class="authorgroup">
<div class="author">
<h3 class="author">
<span class="firstname">Fred</span> <span class="surname">Toussi</span>
</h3>
<div class="affiliation">
<span class="orgname">The HSQL Development Group<br>
</span>
</div>
</div>
</div>
</div>
<div>
<p class="releaseinfo">$Revision: 5746 $</p>
</div>
<div>
<div class="legalnotice" title="Legal Notice">
<a name="N14729"></a>
<p>Copyright 2002-2017 Fred Toussi. Permission is granted to
distribute this document without any alteration under the terms of the
HSQLDB license. Additional permission is granted to the HSQL Development
Group to distribute this document with or without alterations under the
terms of the HSQLDB license.</p>
</div>
</div>
<div>
<p class="pubdate">2017-04-09 14:14:09-0400</p>
</div>
</div>
</div>
<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_modes_tables">Modes of Operation</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_modes_operation">Deployment Types</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#N14755">Database Types</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_table_types">Tables</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_large_objects">Large Objects</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_deploy_context">Deployment context</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_acid_persistence">ACID, Persistence and Reliability</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_acid">Atomicity, Consistency, Isolation, Durability</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#N14818">System Operations</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_backup">Backing Up and Restoring Database Catalogs</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_online_backup">Making Online Backups</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_backup_syntax">Offline Backup Utility Syntax</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_offline_backup">Making Offline Backups</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_listing_backup">Examining Backups</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_restoring_backup">Restoring a Backup</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_encrypted_database">Encrypted Databases</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_encrypted_create">Creating and Accessing an Encrypted Database</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_encrypted_speed">Speed Considerations</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_encrypted_security">Security Considerations</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_monitoring_operation">Monitoring Database Operations</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_external_monitoring">External Statement Level Monitoring</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_internal_monitoring">Internal Statement Level Monitoring</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_internal_event_monitoring">Internal Event Monitoring</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_jdc_logging">Log4J and JDK logging</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_server_monitoring">Server Operation Monitoring</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_database_security">Database Security</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_security_recommend">Basic Security Recommendations</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_security_defaults">Beyond Security Defaults</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_authentication_control">Authentication Control</a></span>
</dt>
</dl>
</dd>
<dt>
<span class="section"><a href="management-chapt.html#mtc_statements">Statements</a></span>
</dt>
<dd>
<dl>
<dt>
<span class="section"><a href="management-chapt.html#mtc_system_operations">System Operations</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_database_settings">Database Settings</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_sql_settings">SQL Conformance Settings</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_cache_persistence">Cache, Persistence and Files Settings</a></span>
</dt>
<dt>
<span class="section"><a href="management-chapt.html#mtc_authntication_settings">Authentication Settings</a></span>
</dt>
</dl>
</dd>
</dl>
</div>
<div class="section" title="Modes of Operation">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_modes_tables"></a>Modes of Operation</h2>
</div>
</div>
</div>
<p>HyperSQL has many modes of operation and features that allow it to
be used in very different scenarios. Levels of memory usage, speed and
accessibility by different applications are influenced by how HyperSQL is
deployed.</p>
<div class="section" title="Deployment Types">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_modes_operation"></a>Deployment Types</h3>
</div>
</div>
</div>
<p>The decision to run HyperSQL as a separate server process or as an
<em class="glossterm">in-process</em> database should be based on the
following:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>When HyperSQL is run as a server on a separate machine, it
is isolated from hardware failures and crashes on the hosts
running the application.</p>
</li>
<li class="listitem">
<p>When HyperSQL is run as a server on the same machine, it is
isolated from application crashes and memory leaks.</p>
</li>
<li class="listitem">
<p>Server connections are slower than
<em class="glossterm">in-process</em> connections due to the overhead
of streaming the data for each JDBC call.</p>
</li>
<li class="listitem">
<p>You can access a Server from outside the main application
and perform backups and other maintenance operations.</p>
</li>
<li class="listitem">
<p>You can reduce client/server traffic using SQL Stored
procedures to reduce the number of JDBC execute calls.</p>
</li>
<li class="listitem">
<p>During development, it is better to use a Server with
server.silent=false, which displays the statements sent to the
server on the console window.</p>
</li>
<li class="listitem">
<p>To improve speed of execution for statements that are
executed repeatedly, reuse a parameterized PreparedStatement for
the lifetime of the connections.</p>
</li>
</ul>
</div>
</div>
<div class="section" title="Database Types">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="N14755"></a>Database Types</h3>
</div>
</div>
</div>
<p>There are three types of database, <code class="literal">mem:</code>,
<code class="literal">file:</code> and <code class="literal">res:</code>. The mem: type is
stored all in memory and not persisted to file. The
<code class="literal">file:</code> type is persisted to file. The
<code class="literal">res:</code> type is also based on files, but the files are
loaded from the classpath, similar to resource and class files. Changes
to the data in <code class="literal">file:</code> databases are persisted, unless
the database is <code class="literal">readonly</code>, or
<code class="literal">files_readonly</code> (using optional property settings).
Changes to <code class="literal">res:</code> databases are not persisted.</p>
<div class="section" title="Readonly Databases">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="mtc_readonly_database"></a>Readonly Databases</h4>
</div>
</div>
</div>
<p>A <em class="glossterm">file:</em> catalog can be made readonly
permanently, or it can be opened as readonly. To make the database
readonly, the property, value pair, <code class="literal">readonly=true</code>
can be added to the <code class="filename">.properties</code> file of the
database. The SHUTDOWN command must be used to close the database
before making this change.</p>
<p>It is also possible to open a normal database as readonly. For
this, the property can be included in the URL of the first connection
to the database.</p>
<p>With readonly databases, it is still possible to insert and
delete rows in TEMP tables.</p>
</div>
<div class="section" title="RES and Files Readonly Databases">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="N14788"></a>RES and Files Readonly Databases</h4>
</div>
</div>
</div>
<p>There is another option which allows MEMORY tables to be
writeable, but without persisting the changes at SHUTDOWN. This option
is activated with the property, value pair,
<code class="literal">files_readonly=true</code>, which can be added to the
<code class="filename">.properties</code> file of the database, or included in
the URL of the first connection to the database.</p>
<p>A <em class="glossterm">res:</em> catalog, is a set of database
files on the classpath (inside a jar or alongside class files). The
database is opened with a URL in the form of
<code class="literal">jdbc:hsqldb:res:<database path></code>. These
databases are always <code class="literal">files_readonly</code> and have the
same restrictions as <code class="literal">files_readonly</code>
<em class="glossterm">file:</em> catalogs.</p>
<p>CACHED tables and LOBS in these catalogs are readonly. It is not
possible to create new LOBs in these catalogs, but you can use
existing LOBs in new rows.</p>
<p>These options are useful for running application tests which
operate on a predefined dataset.</p>
</div>
</div>
<div class="section" title="Tables">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_table_types"></a>Tables</h3>
</div>
</div>
</div>
<p>TEXT tables are designed for special applications where the data
has to be in an interchangeable format, such as CSV (comma separated
values). TEXT tables should not be used for routine storage of data that
changes a lot.</p>
<p>MEMORY tables and CACHED tables are generally used for data
storage. The difference between the two is as follows:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>The data for all MEMORY tables is read from the *.script
file when the database is started and stored in memory. In
contrast the data for cached tables is not read into memory until
the table is accessed. Furthermore, only part of the data for each
CACHED table is held in memory, allowing tables with more data
than can be held in memory.</p>
</li>
<li class="listitem">
<p>When the database is shutdown in the normal way, all the
data for MEMORY tables is written out to the disk. In comparison,
the data in CACHED tables that has changed is written out during
operation and at shutdown.</p>
</li>
<li class="listitem">
<p>The size and capacity of the data cache for all the CACHED
tables is configurable. This makes it possible to allow all the
data in CACHED tables to be cached in memory. In this case, speed
of access is good, but slightly slower than MEMORY tables.</p>
</li>
<li class="listitem">
<p>For normal applications it is recommended that MEMORY tables
are used for small amounts of data, leaving CACHED tables for
large data sets. For special applications in which speed is
paramount and a large amount of free memory is available, MEMORY
tables can be used for large tables as well.</p>
</li>
<li class="listitem">
<p>You can change the type of the table with the <code class="literal">SET
TABLE <table name> TYPE { CACHED | MEMORY
}</code>statement.</p>
</li>
</ul>
</div>
</div>
<div class="section" title="Large Objects">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_large_objects"></a>Large Objects</h3>
</div>
</div>
</div>
<p>HyperSQL 2.0 supports dedicated storage and access to BLOB and
CLOB objects. These objects can have huge sizes. BLOB or CLOB is
specified as the type of a column of the table. Afterwards, rows can be
inserted into the table using a PreparedStatement for efficient transfer
of large LOB data to the database. In <em class="glossterm">mem:</em>
catalogs, CLOB and BLOB data is stored in memory. In
<em class="glossterm">file:</em> catalogs, this data is stored in a single
separate file which has the extension *.lobs. The size of this file can
grow to huge, terabyte figures. By default, a minimum 32 KB is allocated
to each LOB. You can reduced this if your LOBs are generally
smaller.</p>
<p>LOB data should be stored in the database using a JDBC
PreparedStatement object. The streaming methods send the LOB to the
database in one operation as a binary or character stream. Inside the
database, the disk space is allocated as needed and the data is saved as
it is being received. LOB data should be retrieved from the database
using a JDBC ResultSet method. When a streaming method is used to
retrieve a LOB, it is retrieved in large chunks in a transparent manner.
LOB data can also be retrieved as String or byte[], but these methods
use more memory and may not be practical for large objects.</p>
<p>LOB data is not duplicated in the database when a lob is copied
from one table to another. The disk space is reused when a LOB is
deleted and is no longer contained in any table. This happens only at
the time of a CHECKPOINT.</p>
<p>By using a dedicated LOB store, HyperSQL achieves consistently
high speeds (usually over 20MB / s) for both storage and retrieval of
LOBs.</p>
<p>There is an internal LOBS schema in the database to store the
id's, sizes and addresses of the LOBs (but not the actual LOBS) in a few
system tables. This schema is stored in the database as MEMORY tables.
Therefore the amount of JVM memory should be increased when more than
tens of thousands of LOBs are stored in the database. If your database
contains more than a few hundreds of thousands of LOBs and memory use
becomes an issue, you can change one or all LOB schema tables to CACHED
tables. See statements below:</p>
<div class="example">
<a name="N147D8"></a>
<p class="title">
<b>Example 11.1. Using CACHED tables for the LOB schema</b>
</p>
<div class="example-contents">
<pre class="screen"> SET TABLE SYSTEM_LOBS.BLOCKS TYPE CACHED
SET TABLE SYSTEM_LOBS.LOBS TYPE CACHED
SET TABLE SYSTEM_LOBS.PARTS TYPE CACHED
SET TABLE SYSTEM_LOBS.LOB_IDS TYPE CACHED
</pre>
</div>
</div>
<br class="example-break">
</div>
<div class="section" title="Deployment context">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_deploy_context"></a>Deployment context</h3>
</div>
</div>
</div>
<p>The files used for storing HyperSQL database data are all in the
same directory. New files are always created and deleted by the database
engine. Two simple principles must be observed:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>The Java process running HyperSQL must have full privileges on
the directory where the files are stored. This include create and
delete privileges.</p>
</li>
<li class="listitem">
<p>The file system must have enough spare room both for the
'permanent' and 'temporary' files. The default maximum size of the
*.log file is 50MB. The *.data file can grow to up to 64GB (more if
the default has been increased). The .backup file can be up to the
size of the *.data file. The *.lobs file can grow to several
terabytes. The temporary files created at the time of a SHUTDOWN can
be equal in size to the *.script file and the .data file.</p>
</li>
<li class="listitem">
<p>In desktop deployments, virus checker programs may interfere
with the creation and modification of database files. You should
exclude the directory containing the database files from virus
checking.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="section" title="ACID, Persistence and Reliability">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_acid_persistence"></a>ACID, Persistence and Reliability</h2>
</div>
</div>
</div>
<p>HyperSQL's persistence mechanism has proven reliable, as the last
critical issue was fixed 2 years before the release of version 2.0.</p>
<p>There are further enhancements in the latest version.</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>More extensive locking mechanism has been added to code to
support multithreaded access.</p>
</li>
<li class="listitem">
<p>Incremental backup (an internal mechanism for crash protection)
allows fast checkpoint and shutdown.</p>
</li>
<li class="listitem">
<p>All files are synced at checkpoints and also just before
closing.</p>
</li>
<li class="listitem">
<p>The data file is enlarged in block increments</p>
</li>
<li class="listitem">
<p>The NIO file access implementation has been improved</p>
</li>
</ul>
</div>
<p>Persistence relies on the JVM, the operating system, and the
computer hardware. A database system like HSQLDB can perform millions of
read and write operations in an hour. As system hardware and software can
go wrong, it is impossible to achieve zero failure rate. Therefore regular
backups are recommended. HyperSQL 2.3 has built-in database backup and
restore features, discussed elsewhere in this chapter.</p>
<p>A note regarding the NIO file access implementation: This
implementation applies only to CACHED table data in the
<code class="literal">.data</code> file. Other files are not accessed via NIO. There
has been an issue with some JVM implementations of nio not releasing the
file buffers after they were closed. HyperSQL uses a workaround which is
recommended for Sun JVM's. This does not apply to other JVM's. In such
environments, it is therefore recommended to test the CHECKPOINT DEFRAG
operation and the shutting down and restarting the database inside the
same Java process extensively with NIO. Use of NIO is not essential and
can be turned off if necessary.</p>
<div class="section" title="Atomicity, Consistency, Isolation, Durability">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_acid"></a>Atomicity, Consistency, Isolation, Durability</h3>
</div>
</div>
</div>
<p>Atomicity means a transaction either fails without changing the
data, or succeeds. HyperSQL ensures atomicity both during operations and
in the event of a system crash.</p>
<p>Consistency means all the implicit and explicit integrity
constraints are always enforced. HyperSQL always enforces the
constraints and at the same time does not allow unenforceable
constraints (illegal forms of CHECK constraints) to be created.</p>
<p>Isolation means transactions do not interfere with each other.
HyperSQL enforces isolation according to strict rules of the database
isolation model (MVCC or LOCKS).</p>
<p>Durability means a committed transaction is protected in case of a
system crash. HyperSQL ensures durability according to the setting for
WRITE DELAY MILLIS. A zero delay setting results in an
FileDescriptor#sync() call each time a transaction commits. A timed
delay means the FileDescriptor#sync() call is executed in the given
intervals and only the last transactions committed in the time interval
may be lost. The default time interval is 0.5 second. The sync() call is
also made at all critical points, including when a file is about to be
closed. Durability of files requires a reliable JVM and disk storage
system that stores the data safely with a sync() call. In practice, many
systems are generally reliable in this respect.</p>
</div>
<div class="section" title="System Operations">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="N14818"></a>System Operations</h3>
</div>
</div>
</div>
<p>A database is opened when the first connection is successfully
made. It remains open until the <code class="literal">SHUTDOWN</code> command is
issued. If the connection property shutdown=true is used for the first
connection to the database, the database is shutdown when the last
connection is closed. Otherwise the database remains open and will
accept the next connection attempt.</p>
<p>The <code class="literal">SHUTDOWN</code> command shuts down the database
properly and allows the database to be reopened quickly. This command
may take some seconds as it saves all the modified data in the
.<code class="literal">script</code> and <code class="literal">.data</code> files. Variants
of <code class="literal">SHUTDOWN</code> such as <code class="literal">SHUTDOWN
COMPACT</code> and <code class="literal">SHUTDOWN SCRIPT</code> can be used
from time to time to reduce the overall size of the database files.
Another variant is <code class="literal">SHUTDOWN IMMEDIATELY</code> which ensures
all changes to data are stored in the <code class="literal">.log</code> file but
does not save the changes in .<code class="literal">script</code> and
<code class="literal">.data</code> files. The shutdown is performed quickly but
the database will take much longer to reopen.</p>
<p>During the lifetime of the database the checkpoint operation may
be performed from time to time. The <code class="literal">SET FILES LOG SIZE <
value ></code> setting and its equivalent URL property determine
the frequency of automatic checkpoints. An online backup also performs a
checkpoint when the backup is not a hot backup. A checkpoint can be
performed by the user at any time using the
<code class="literal">CHECKPOINT</code> statement. The main purpose of checkpoints
is to reduce the total size of database files and to allow a quick
restart in case the database is closed without a proper shutdown. The
<code class="literal">CHECKPOINT DEFRAG</code> variant compacts the
<code class="literal">.data</code> file in a similar way to <code class="literal">SHUTDOWN
COMPACT</code> does. Obviously this variant takes much longer than a
normal <code class="literal">CHECKPOINT</code>. A database setting allows a
<code class="literal">CHECKPOINT DEFRAG</code> to be performed automatically when
wasted space in the <code class="literal">.data</code> file exceeds the specified
percentage.</p>
<p>In a multi-user application, automatic or user-initiated
checkpoints are delayed until all other sessions have committed or
rolled back. During a checkpoint, other sessions cannot access the
database tables but can access the <code class="literal">INFORMATION_SCHEMA</code>
system tables.</p>
</div>
</div>
<div class="section" title="Backing Up and Restoring Database Catalogs">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_backup"></a>Backing Up and Restoring Database Catalogs</h2>
</div>
</div>
</div>
<a name="N14863" class="indexterm"></a>
<p>The database engine saves the files containing all the data in a
file catalog when a shutdown takes place. It automatically recovers from
an abnormal termination and preserves the data when the catalog is opened
next time. In an ideal operating environment, where there is no OS crash,
disk failure, bugs in code, etc. there would be no need to backup a
database. Backing up catalogs is an insurance policy against all sorts of
misadventure that are not under the control of the database engine.</p>
<p>The data for each catalog consists of up to 5 files in the same
directory with the endings such as <code class="literal">*.properties</code>,
<code class="literal">*.script</code>, etc., as detailed in previous
chapters.</p>
<p>HyperSQL 2 includes commands to backup the database files into a
single <code class="literal">.tar</code> or <code class="literal">.tar.gz</code> file archive,
or alternatively as copies of the database files. The backup can be
performed by a command given in a JDBC session if the target database
catalog is running, or on the command-line if the target catalog has been
shutdown.</p>
<p>It is not recommended to backup the database file with an
external file backup program while the database is running. The resulting
backup will probably be inconsistent and not useful for restoring the
database</p>
<div class="section" title="Making Online Backups">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_online_backup"></a>Making Online Backups</h3>
</div>
</div>
</div>
<p>To back up a running catalog, obtain a JDBC connection and
issue a <code class="literal">BACKUP DATABASE</code> command in SQL. In its most
simple form, the command format below will backup the database as a
single <code class="literal">.tar.gz</code> file to the given directory. This type
of backup performs a checkpoint immediately before backing up the
files.</p>
<pre class="programlisting"> BACKUP DATABASE TO <directory name> BLOCKING [ AS FILES ]</pre>
<p>The <span class="emphasis"><em>directory name</em></span> must end with a slash
to distinguish it as a directory, and the whole string must be in single
quotes like so: <code class="literal">'subdir/nesteddir/'</code>.</p>
<p>Normal backup may take a long time with very large databases.
Hot backup may be used in those situations. This type of backup does not
perform a checkpoint and allows access to the database while backup is
in progress.</p>
<pre class="programlisting"> BACKUP DATABASE TO <directory name> NOT BLOCKING [ AS FILES ]</pre>
<p>If you add AS FILES to the statements, the database files are
backed up as separate files in the directory, without any gzip
compression or tar archiving.</p>
<p>See the next section under Statements for details about the
command and its options. See the sections below about restoring a
backup.</p>
</div>
<div class="section" title="Offline Backup Utility Syntax">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_backup_syntax"></a>Offline Backup Utility Syntax</h3>
</div>
</div>
</div>
<p>The <code class="classname">DbBackup</code> class is used from the
command-line to make offline backups and to restore backups. Here is how
to see all options for <code class="classname">DbBackup</code>. </p>
<div class="example">
<a name="N148A5"></a>
<p class="title">
<b>Example 11.2. Displaying DbBackup Syntax</b>
</p>
<div class="example-contents">
<pre class="screen"> java -cp hsqldb.jar org.hsqldb.lib.tar.DbBackupMain</pre>
</div>
</div>
<p>
<br class="example-break">
</p>
</div>
<div class="section" title="Making Offline Backups">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_offline_backup"></a>Making Offline Backups</h3>
</div>
</div>
</div>
<p>To back up an offline catalog, the catalog must be in shut down
state. You will run a Java command like this. In this example, the
database is named dbname and is in the dbdir directory. The backup is
saved to a file named backup.tar in the tardir directory.</p>
<div class="example">
<a name="N148B0"></a>
<p class="title">
<b>Example 11.3. Offline Backup Example</b>
</p>
<div class="example-contents">
<pre class="screen"> java -cp hsqldb.jar org.hsqldb.lib.tar.DbBackupMain --save tardir/backup.tar dbdir/dbname</pre>
</div>
</div>
<p>
<br class="example-break">where <code class="filename">tardir/backup.tar</code> is a file path
to the <code class="literal">*.tar</code> or <code class="literal">*.tar.gz</code> file to
be created in your file system, and <code class="filename">dbdir/dbname</code> is
the file path to the catalog file base name (in same fashion as in
<code class="varname">server.database.*</code> settings and JDBC URLs with catalog
type <em class="glossterm">file:</em>.</p>
</div>
<div class="section" title="Examining Backups">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_listing_backup"></a>Examining Backups</h3>
</div>
</div>
</div>
<p>You can list the contents of backup tar files with
<code class="classname">DbBackup</code> on your operating system command line,
or with any Pax-compliant tar or pax client (this includes GNU tar),
</p>
<div class="example">
<a name="N148D1"></a>
<p class="title">
<b>Example 11.4. Listing a Backup with DbBackup</b>
</p>
<div class="example-contents">
<pre class="screen"> java -cp hsqldb.jar org.hsqldb.lib.tar.DbBackupMain --list tardir/backup.tar</pre>
</div>
</div>
<p>
<br class="example-break">You can also give regular expressions at the end of the
command line if you are only interested in some of the file entries in
the backup. Note that these are real regular expressions, not shell
globbing patterns, so you would use <code class="literal">.+script</code> to match
entries ending in "script", not <code class="literal">*script</code>.</p>
<p>You can examine the contents of the backup in their entirety by
restoring the backup, as explained in the following section, to a
temporary directory.</p>
</div>
<div class="section" title="Restoring a Backup">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_restoring_backup"></a>Restoring a Backup</h3>
</div>
</div>
</div>
<p>You use <code class="classname">DbBackup</code> on your operating system
command line to restore a catalog from a backup. </p>
<div class="example">
<a name="N148E8"></a>
<p class="title">
<b>Example 11.5. Restoring a Backup with DbBackup</b>
</p>
<div class="example-contents">
<pre class="screen"> java -cp hsqldb.jar org.hsqldb.lib.tar.DbBackupMain --extract tardir/backup.tar dbdir</pre>
</div>
</div>
<p>
<br class="example-break">where <code class="filename">tardir/backup.tar</code> is a file path
to the *.tar or *.tar.gz file to be read, and <code class="filename">dbdir</code>
is the target directory to extract the catalog files into. Note that
<code class="filename">dbdir</code> specifies a directory path, without the
catalog file base name. The files will be created with the names stored
in the tar file (and which you can see as described in the preceding
section). After restoring the database, you can connect to it as
usual.</p>
</div>
</div>
<div class="section" title="Encrypted Databases">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_encrypted_database"></a>Encrypted Databases</h2>
</div>
</div>
</div>
<p>HyperSQL supports encrypted databases. Encryption services use the
Java Cryptography Extensions (JCE) and uses the ciphers installed with the
JRE. HyperSQL itself does not contain any cryptography code.</p>
<p>Three elements are involved in specifying the encryption method and
key. A cipher, together with its configuration is identified by a string
which includes the name of the cipher and optional parameters. A provider
is the fully qualified class name of the cipher provider. A key is
represented as a hexadecimal string.</p>
<div class="section" title="Creating and Accessing an Encrypted Database">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_encrypted_create"></a>Creating and Accessing an Encrypted Database</h3>
</div>
</div>
</div>
<p>First, a key must be created for the desired cipher and
configuration. This is done by calling the function CRYPT_KEY(<cipher
spec>, <provider>). If the default provider (the built-in JVM
ciphers) is used, then NULL should be specified as the provider. The
CRYPT_KEY function returns a hexadecimal key. The function call can be
made in any HyperSQL database, so long as the provider class is on the
classpath. This key can be used to create a new encrypted database.
Calls to this function always return different keys, based on generated
random values.</p>
<p>As an example, a call to CRYPT_KEY('Blowfish', null) returned the
string, '604a6105889da65326bf35790a923932'. To create a new database,
the URL below is used:</p>
<p>
<code class="literal">jdbc:hsqldb:file:<database
path>;crypt_key=604a6105889da65326bf35790a923932;crypt_type=blowfish</code>
</p>
<p>The third property name is crypt_provider. This is specified only
when the provider is not the default provider.</p>
<p>HyperSQL works with any symmetric cipher that may be available
from the JVM.</p>
<p>The files that are encrypted include the .script, .data, .backup
and .log files. The .lobs file is not encrypted by default. The property
crypt_lobs=true must be specified to encrypt the .lobs file. When this
property is used, the blobs and clobs are both compressed and
encrypted.</p>
</div>
<div class="section" title="Speed Considerations">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_encrypted_speed"></a>Speed Considerations</h3>
</div>
</div>
</div>
<p>General operations on an encrypted database are performed the same
as with any database. However, some operations are significantly slower
than with the equivalent cleartext database. With MEMORY tables, there
is no difference to the speed of SELECT statements, but data change
statements are slower. With CACHED tables, the speed of all statements
is slower.</p>
</div>
<div class="section" title="Security Considerations">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_encrypted_security"></a>Security Considerations</h3>
</div>
</div>
</div>
<p>Security considerations for encrypted databases have been
discussed at length in HSQLDB discussion groups. Development team
members have commented that encryption is not a panacea for all security
needs. The following issues should be taken into account:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>Encrypted files are relatively safe in transport, but
because databases contain many repeated values and words,
especially known tokens such as CREATE, INSERT, etc., breaking the
encryption of a database may be simpler than an unknown
file.</p>
</li>
<li class="listitem">
<p>Only the files are encrypted, not the memory image. Poking
into computer memory, while the database is open, will expose the
contents of the database.</p>
</li>
<li class="listitem">
<p>HyperSQL is open source. Someone who has the key, can
compile and use a modified version of the program that saves a
full cleartext dump of an encrypted database</p>
</li>
</ul>
</div>
<p>Therefore encryption is generally effective only when
the users who have access to the crypt key are trusted.</p>
</div>
</div>
<div class="section" title="Monitoring Database Operations">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_monitoring_operation"></a>Monitoring Database Operations</h2>
</div>
</div>
</div>
<p>Database operations can be monitored at different levels using
internal HyperSQL capabilities or add-ons.</p>
<div class="section" title="External Statement Level Monitoring">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_external_monitoring"></a>External Statement Level Monitoring</h3>
</div>
</div>
</div>
<p>Statement level monitoring allows you to gather statistics about
executed statements. HyperSQL is supported by the monitoring tool JAMon
(Java Application Monitor). JAMon is currently developed as the
SourceForge project, jamonapi.</p>
<p>JAMon works at the JDBC level. It can monitor and gather
statistics on different types of executed statements or other JDBC
calls.</p>
<p>Early versions of JAMon were developed with HSQLDB and had to be
integrated into HSQLDB at code level. The latest versions can be added
on as a proxy in a much simpler fashion.</p>
</div>
<div class="section" title="Internal Statement Level Monitoring">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_internal_monitoring"></a>Internal Statement Level Monitoring</h3>
</div>
</div>
</div>
<p>The internally-generated, individual sql log for the database can
be enabled with the <code class="literal">SET DATABASE EVENT LOG SQL LEVEL</code>
statement, described in this chapter. As all the executed statements are
logged, there is an impact on speed. So you should only use this for
debugging. Two levels of sql logging are supported.</p>
</div>
<div class="section" title="Internal Event Monitoring">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_internal_event_monitoring"></a>Internal Event Monitoring</h3>
</div>
</div>
</div>
<p>HyperSQL can log important internal events of the engine. These
events occur during the operation of the engine, and are not always
coupled with the exact type of statement being executed. Normal events
such as opening and closing of files, or errors such as OutOfMemory
conditions are examples of logged events.</p>
<p>HyperSQL supports two methods of logging. One method is specific
to the individual database and is managed internally by HyperSQL. The
other method is specific to JVM and is managed by a logging
framework.</p>
<p>The internally-generated, individual log for the database can be
enabled with the <code class="literal">SET DATABASE EVENT LOG LEVEL</code>
statement, described in this chapter. This method of logging is very
useful for desktop application deployment, as it provides an ongoing
record of database operations.</p>
</div>
<div class="section" title="Log4J and JDK logging">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_jdc_logging"></a>Log4J and JDK logging</h3>
</div>
</div>
</div>
<p>HyperSQL also supports log4J and JDK logging. The same event
information that is passed to the internal log, is passed to external
logging frameworks. These frameworks are typically configured outside
HyperSQL. The log messages include the string "hsqldb.db." followed by
the unique id (a 16 character string) of the database that generated the
message, so they can be identified in a multi-database server
context.</p>
<p>As the default JDK logging framework has several shortcomings,
HyperSQL configures this logging framework for better operation. If you
do not want HyperSQL to configure the JDK logging framework, you should
include the system level property
<code class="literal">hsqldb.reconfig_logging=false</code> in your
environment.</p>
</div>
<div class="section" title="Server Operation Monitoring">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_server_monitoring"></a>Server Operation Monitoring</h3>
</div>
</div>
</div>
<p>A Server or WebServer instance can be started with the property
server.silent=false. This causes all the connections and their executed
statements to be printed to stdout as the statements are submitted to
the server.</p>
</div>
</div>
<div class="section" title="Database Security">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_database_security"></a>Database Security</h2>
</div>
</div>
</div>
<p>HyperSQL has extensive security features which are implemented at
different levels and covered in different chapters of this guide.</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>The server can use SSL and IP address access control lists. See
the <a class="link" href="listeners-chapt.html" title="Chapter 14. HyperSQL Network Listeners (Servers)">HyperSQL Network Listeners
(Servers)</a> chapter.</p>
</li>
<li class="listitem">
<p>You can define a system property to stop the database engine
accessing the Java static functions that are on the classpath, apart
from a limited set that you allow. See Securing Access to Classes in
the <a class="link" href="sqlroutines-chapt.html" title="Chapter 8. SQL-Invoked Routines">SQL-Invoked Routines</a> chapter.</p>
</li>
<li class="listitem">
<p>You can define a system property to allow access to files on the
file system outside the database directory and its children. This
access is only necessary if you use TEXT tables or want to load and
save files directly to the file system as BLOB or CLOB. See the <a class="link" href="texttables-chapt.html" title="Chapter 5. Text Tables">Text Tables</a>
chapter.</p>
</li>
<li class="listitem">
<p>The database files can be encrypted. Discussed in this
chapter.</p>
</li>
<li class="listitem">
<p>Within the database, the DBA privileges are required for system
and maintenance jobs.</p>
</li>
<li class="listitem">
<p>You can define users and roles and grant them access on
different database objects. Each user has a password and is granted a
set of privileges. HSQLDB supports table level and column level
privileges. See the <a class="link" href="accesscontrol-chapt.html" title="Chapter 6. Access Control">Access Control</a> chapter.</p>
</li>
<li class="listitem">
<p>You can define a password complexity check function for new and
changed passwords. This is covered below under Authentication
Settings.</p>
</li>
<li class="listitem">
<p>You can use external authentication such as LDAP instead of
internally stored password to authenticate users for each database.
This is covered below under Authentication Settings.</p>
</li>
</ol>
</div>
<p>HyperSQL security is multi-layered and avoids any loopholes to
circumvent security. It is however the user's responsibility to enable the
required level of security.</p>
<div class="section" title="Basic Security Recommendations">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_security_recommend"></a>Basic Security Recommendations</h3>
</div>
</div>
</div>
<p>The default setting are generally adequate for embedded use of the
database in single-user applications. For servers on the host that are
accessed from the same machine or accessed within a network, and
especially for those accessed from outside the network, additional
security settings must be used. This is the minimum list of changes you
need to make:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>Change the admin password. Change the admin name (the default
is SA) as well for extra security.</p>
</li>
<li class="listitem">
<p>Create a non-admin user for normal database access and grant
the required SELECT, INSERT, UPDATE and DELETE privileges to this
user. Connect with this user's credentials from the
application.</p>
</li>
<li class="listitem">
<p>Set up SSL and IP address access control on the Server.</p>
</li>
<li class="listitem">
<p>Restrict the execution of multiple statements with
<code class="literal">SET DATABASE SQL RESTRICT EXEC TRUE</code> .</p>
</li>
<li class="listitem">
<p>Backup the database regularly and store the backups in a
different location than the machine running the Server.</p>
</li>
</ul>
</div>
</div>
<div class="section" title="Beyond Security Defaults">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_security_defaults"></a>Beyond Security Defaults</h3>
</div>
</div>
</div>
<p>The default settings for server and web server do not use SSL or
IP access control lists. These features are enabled programatically, or
with the properties used to start the server.</p>
<p>The default settings allow a database user with the DBA role or
with schema creation role to access static functions on the classpath.
You can disable this feature or limit it to specific classes and
methods. This can be done programatically or by setting a system
property when you start a server.</p>
<p>If access to specific static functions is granted, then these
functions must be considered as part of the database program and checked
for any security flaws before inclusion in the classpath.</p>
<p>The default settings do not allow a user to access files outside
the database directory. This access is for TEXT table source files. You
can override this programatically or with a system property when you
start a server.</p>
<p>The encryption of database file does not utilise any user-supplied
information for encryption keys. This level of security is outside the
realm of users and passwords.</p>
<p>The first user for a new database has the DBA role. This user name
was always SA in older versions of HSQLDB, but not in the latest
versions. The name of the first DBA user and its password can be
specified when the database is created by the first connection to the
database. These settings are then stored in the database. You can also
change the name after creating the database.</p>
<p>The initial user with the DBA role should be used for admin
purposes only. At least one additional role should be created for normal
database use in the application and at least one additional user should
be created and granted this role. The new role should not be given the
DBA role. It can be given the CREATE_SCHEMA role, which allows it to
create and access multiple schemas. Alternatively, the user with the DBA
role can create the schemas and their objects and then grant specific
privileges on the objects to the non-DBA role.</p>
</div>
<div class="section" title="Authentication Control">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_authentication_control"></a>Authentication Control</h3>
</div>
</div>
</div>
<p>Authentication is the mechanism that determines if a user can
access the database at all. Once authentication is performed, the
authorization mechanism is used to determine which database objects the
particular user can access. The default authentication mechanism is
password authentication. Each user is created with a password, which is
stored as a hash in the database and checked each time a new database
connection is created.</p>
<a name="N149C1" class="indexterm"></a>
<p>
<span class="bold"><strong>Password Complexity
Check</strong></span>
</p>
<p>HyperSQL allows you to define a function that checks the quality
of the passwords defined in the database. The passwords are stored in
the database. Each time a user connects, the user's name and password
are checked against the stored list of users and passwords. The
connection attempt is rejected if there is no match.</p>
<a name="N149CC" class="indexterm"></a>
<p>
<span class="bold"><strong>External
Authentication</strong></span>
</p>
<p>You can use an external authentication mechanism instead of the
internal authentication mechanism. HyperSQL allows you to define a
function that checks the combination of database unique name, user name,
and password for each connection attempt. The function can use external
resources to authenticate the user. For example, a directory server may
be used. The password may be ignored if the external resource can verify
the user's credential without it.</p>
<p>You can override external authentication for a user with the ALTER
USER statement. See the <a class="link" href="accesscontrol-chapt.html" title="Chapter 6. Access Control">Access Control</a> chapter</p>
</div>
</div>
<div class="section" title="Statements">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="mtc_statements"></a>Statements</h2>
</div>
</div>
</div>
<p>System level statements are listed in this section. Statements that
begin with SET DATABASE or SET FILES are for properties that have an
effect on the normal operation of HyperSQL. The effects of these
statements are also discussed in different chapters.</p>
<div class="section" title="System Operations">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_system_operations"></a>System Operations</h3>
</div>
</div>
</div>
<p>These statements perform a system level action.</p>
<a name="N149E9" class="indexterm"></a>
<p>
<span class="bold"><strong>SHUTDOWN</strong></span>
</p>
<p>
<span class="emphasis"><em>shutdown statement</em></span>
</p>
<p>
<code class="literal"><shutdown statement> ::= SHUTDOWN [IMMEDIATELY |
COMPACT | SCRIPT]</code>
</p>
<p>Shutdown the database. If the optional qualifier is not used, a
normal SHUTDOWN is performed. A normal SHUTDOWN ensures all data is
saved correctly and the database opens without delay on next
use.</p>
<div class="variablelist">
<table border="0">
<col valign="top" align="left">
<tbody>
<tr>
<td>
<p>
<span class="term">SHUTDOWN</span>
</p>
</td><td>
<p>Normal shutdown saves all the database files, then deletes
the .log file (and the .backup file in the default mode). This
does the same thing as CHECKPOINT, but closes the database when it
completes. The database opens without delay on next used.</p>
</td>
</tr>
<tr>
<td>
<p>
<span class="term">SHUTDOWN IMMEDIATELY</span>
</p>
</td><td>
<p>Saves the *.log file and closes the database files. This is
the quickest form of shutdown. This command should not be used as
the routine method of closing the database, because when the
database is accessed next time, it may take a long time to
start.</p>
</td>
</tr>
<tr>
<td>
<p>
<span class="term">SHUTDOWN COMPACT</span>
</p>
</td><td>
<p>This is similar to normal SHUTDOWN, but reduces the *.data
file to its minimum size. It can take much longer than normal
SHUTDOWN. This shouldn't be used as routine.</p>
</td>
</tr>
<tr>
<td>
<p>
<span class="term">SHUTDOWN SCRIPT</span>
</p>
</td><td>
<p>This is similar to SHUTDOWN COMPACT, but it does not rewrite
the <code class="literal">*.data</code> and text table files. After SHUTDOWN
SCRIPT, only the <code class="literal">*.script</code> and
<code class="literal">*.properties</code> files remain. At the next startup,
these files are processed and the <code class="literal">*.data</code> file
is created if there are cached tables. This command in effect
performs part of the job of SHUTDOWN COMPACT, leaving the other
part to be performed automatically at the next startup.</p>
<p>This command produces a full script of the database which
can be edited for special purposes prior to the next
startup.</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N14A23" class="indexterm"></a>
<p>
<span class="bold"><strong>BACKUP DATABASE</strong></span>
</p>
<p>
<span class="emphasis"><em>backup database statement</em></span>
</p>
<p>
<code class="literal"><backup database statement> ::= BACKUP DATABASE
TO <file path> [SCRIPT] {[NOT] COMPRESSED} {[NOT] BLOCKING} [AS
FILES]</code>
</p>
<p>Backup the database to specified <code class="literal"><file
path></code> for archiving purposes.</p>
<p>The <code class="literal"><file path></code> can be in two forms.
If the <code class="literal"><file path></code> ends with a forward slash,
it specifies a directory. In this case, an automatic name for the
archive is generated that includes the date, time and the base name of
the database. The database is backed up to this archive file in the
specified directory. The archive is in <code class="literal">.tar.gz</code> or
<code class="literal">.tar</code> format depending on whether it is compressed or
not.</p>
<p>If the <code class="literal"><file path></code> does not end with a
forward slash, it specifies a user-defined file name for the backup
archive. The file extension must be either <code class="literal">.tar.gz</code> or
<code class="literal">.tar</code> and this must match the compression
option.</p>
<p>The default set of options is COMPRESSED BLOCKING.</p>
<p>If SCRIPT is specified, the backup will contain a
<code class="literal">*.script</code> file, which contain all the data and
settings of the database. This type of backup is suitable for smaller
databases. With larger databases, this takes a long time. When the
SCRIPT option is no used, the backup set will consist of the current
snapshot of all database files.</p>
<p>If NOT COMPRESSED is specified, the backup is a tar file,
without compression. Otherwise, it is in gzip format.</p>
<p>The qualifier, BLOCKING, means all database operations are
suspended during backup. During backup, a CHECKPOINT command is silently
executed. This mode is always used when SCRIPT is specified.</p>
<p>Hot backup is performed if NOT BLOCKING is specified. In this
mode, the database can be used during backup. This mode should only be
used with very large databases. A hot backup set is less compact and
takes longer to restore and use than a normal backup set produced with
the BLOCKING option. You can perform a CHECKPOINT just before a hot
backup in order to reduce the size of the backup set.</p>
<p>If AS FILES is specified, the database files are copied to a
directory specified by <file path> without any compression. The
file path must be a directory. If the directory does not exist, it is
created. The file path may be absolute or relative. If it is relative,
it is interpreted as relative to the location of database files. When AS
FILES is specified, SCRIPT or COMPRESSED options are not available. The
backup can be performed as BLOCKING or NOT BLOCKING.</p>
<p>The HyperSQL jar also contains a program that creates an
archive of an offline database. It also contains a program to expand an
archive into database files. These programs are documented in this
chapter under Backing up Database Catalogs.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N14A63" class="indexterm"></a>
<p>
<span class="bold"><strong>CHECKPOINT</strong></span>
</p>
<p>
<span class="emphasis"><em>checkpoint statement</em></span>
</p>
<p>
<code class="literal"><checkpoint statement> ::= CHECKPOINT
[DEFRAG]</code>
</p>
<p>Closes the database files, rewrites the script file, deletes
the log file and reopens the database.</p>
<p>If <code class="literal">DEFRAG</code> is specified, also shrinks the
<code class="literal">*.data</code> file to its minimum size. <code class="literal">CHECKPOINT
DEFRAG</code> time depends on the size of the database and can take a
long time with huge databases.</p>
<p>A checkpoint on a multi-user database waits until all other
sessions have committed or rolled back. While the checkpoint is in
progress other sessions are kept waiting. Checkpoint does not close any
sessions.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N14A83" class="indexterm"></a>
<p>
<span class="bold"><strong>SCRIPT</strong></span>
</p>
<p>
<span class="emphasis"><em>script statement</em></span>
</p>
<p>
<code class="literal"><script statement> ::= SCRIPT [<file
name>]</code>
</p>
<p>Returns a script containing SQL statements that define the
database, its users, and its schema objects. If <code class="literal"><file
name></code> is not specified, the statements are returned in a
ResultSet, with each row containing an SQL statement. No data statements
are included in this form. The optional file name is a single-quoted
string. If <code class="literal"><file name></code> is specified, then the
script is written to the named file. In this case, all the data in all
tables of the database is included in the script as INSERT
statements.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
</div>
<div class="section" title="Database Settings">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_database_settings"></a>Database Settings</h3>
</div>
</div>
</div>
<p>These statements change the database settings.</p>
<a name="N14AA2" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE
COLLATION</strong></span>
</p>
<p>
<span class="emphasis"><em>set database collation statement</em></span>
</p>
<p>
<code class="literal"><set database collation statement> ::= SET
DATABASE COLLATION <collation name> [ NO PAD | PAD SPACE
]</code>
</p>
<p>Each database can have its own default collation. Sets the
collation from the set of collations supported by HyperSQL. Once this
command has been issued, the database can be opened in any JVM and will
retain its collation.</p>
<p>All collations pad the shorter string with spaces when two
strings are compared. If NO PAD is specified, comparison is performed
without padding. The default system collation is named
<code class="literal">SQL_TEXT</code>. To use the default without padding use
<code class="literal">SET DATABASE COLLATION SQL_TEXT NO PAD</code>.</p>
<p>After you change the collation for a database that contains
collated data, you must execute <code class="literal">SHUTDOWN COMPACT</code> or
<code class="literal">SHUTDOWN SCRIPT</code> in order to recreate the
indexes.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>Collations are discussed in the <a class="link" href="databaseobjects-chapt.html" title="Chapter 4. Schemas and Database Objects">Schemas and Database Objects</a> chapter. Some examples of
setting the database collation follow:</p>
<pre class="programlisting"> -- this collation is an ascii collation with Upper Case Comparison (coverts strings to uppercase for comparison)
SET DATABASE COLLATION SQL_TEXT_UCC
-- this collation is case-insensitive English
SET DATABASE COLLATION "English 1"
-- this collation is case-sensitive French
SET DATABASE COLLATION "French 2" </pre>
<a name="N14ACE" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE DEFAULT RESULT MEMORY
ROWS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database default result memory rows
statement</em></span><code class="literal"> </code>
</p>
<p>
<code class="literal"><set database default result memory rows> ::=
SET DATABASE DEFAULT RESULT MEMORY ROWS <unsigned integer
literal></code>
</p>
<p>Sets the maximum number of rows of each result set and internal
temporary table that is held in memory. Temporary tables includes views,
schema-based and session-based TEMPORARY tables, transient tables for
subqueries, and <code class="literal">INFORMATION_SCHEMA</code> tables.</p>
<p>This setting applies to all sessions. Individual sessions can
change the value with the <code class="literal">SET SESSION RESULT MEMORY
ROWS</code> statement. The default is 0, meaning all result sets are
held in memory.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.result_max_memory_rows</code>.</p>
<a name="N14AF0" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE DEFAULT TABLE
TYPE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database default table type
statement</em></span><code class="literal"> </code>
</p>
<p>
<code class="literal"><set database default table type> ::= SET
DATABASE DEFAULT TABLE TYPE { CACHED | MEMORY }</code>
</p>
<p>Sets the type of table created when the next CREATE TABLE
statement is executed. The default is MEMORY.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.default_table_type</code>.</p>
<a name="N14B0A" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE EVENT LOG
LEVEL</strong></span>
</p>
<p>
<span class="emphasis"><em>set database event log level
statement</em></span>
</p>
<p>
<code class="literal"><set database event log level> ::= SET DATABASE
EVENT LOG [ SQL ] LEVEL { 0 | 1 | 2 | 3 }</code>
</p>
<p>When the SQL option is not used, this statement sets the amount
of information logged in the internal, database-specific event log.
Level 0 means no log. Level 1 means only important (error) events. Level
2 means more events, including both important and less important
(normal) events. Level 3 includes even more details. For readonly and
<em class="glossterm">mem:</em> databases, if the level is set above 0, the
log messages are directed to stderr.</p>
<p>The events are logged in a file with the extension
<code class="literal">.app.log</code> alongside the main database files.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.applog</code>.</p>
<p>When the SQL option is used, this statement logs the SQL
statements as they are executed. Each log line contains the timestamp
and the session number, followed by the SQL statement and JDBC arguments
if any.</p>
<p>Levels 1, 2 and 3 are supported. Level 1 only logs commits and
rollbacks, while Level 2 and 3 log all statements. Level 2 truncates
long statements, while level 3 reports the full statement and parameter
values.</p>
<p>The logged lines are stored in a file with the extension
<code class="literal">.sql.log</code> alongside the main database files.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.sqllog</code>.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>From version 2.3, the equivalent URL properties,
<code class="literal">hsqldb.app_log</code> and <code class="literal">hsqldb.sql_log</code>,
can be used not only for a new database, but also when opening an
existing file database to change the event log level.</p>
<p>An extract from an .sql.log file created with log Level 3 is
shown below. The numbers after the timestamp (10 and 1) show the session
number. The values for prepared statement parameters are shown in
parentheses at the end of the statement.</p>
<div class="example">
<a name="N14B42"></a>
<p class="title">
<b>Example 11.6. SQL Log Example</b>
</p>
<div class="example-contents">
<pre class="screen"> 2012-11-29 10:40:40.250 10 INSERT INTO TEST_CLOB VALUES (1,'Ut wisi enim ad minim veniam, quis nostrud exerci')
2012-11-29 10:40:40.250 1 INSERT INTO SYSTEM_LOBS.LOB_IDS VALUES(?, ?, ?, ?) (1,49,0,40)
2012-11-29 10:40:40.250 1 COMMIT
2012-11-29 10:40:40.265 1 CALL SYSTEM_LOBS.ALLOC_BLOCKS(?, ?, ?) (1,0,1)
2012-11-29 10:40:40.265 1 COMMIT
</pre>
</div>
</div>
<br class="example-break">
<a name="N14B47" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE GC</strong></span>
</p>
<p>
<span class="emphasis"><em>set database gc statement</em></span>
</p>
<p>
<code class="literal"><set database gc statement> ::= SET DATABASE GC
<unsigned integer literal></code>
</p>
<p>An optional property which forces calls to <code class="literal">System.gc()
</code>after the specified number of row operations. The default
value for this property is 0, which means no System.gc() calls. Usual
values for this property range from 10000 depending on the system and
the memory allocation. This property may be useful in some in-process
deployments, especially with older JVM implementations.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N14B5D" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE TEXT TABLE
DEFAULTS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database text table defaults
statement</em></span>
</p>
<p>
<code class="literal"><set database text table defaults statement> ::=
SET DATABASE TEXT TABLE DEFAULTS <character
literal></code>
</p>
<p>An optional property to override default text table settings.
The string literal has the same format as the string used for setting
the data source of a text table, but without the file name. See the
<a class="link" href="texttables-chapt.html" title="Chapter 5. Text Tables">Text Tables</a>
chapter.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N14B74" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE TRANSACTION
CONTROL</strong></span>
</p>
<p>
<span class="emphasis"><em>set database transaction control
statement</em></span>
</p>
<p>
<code class="literal"><set database transaction control statement> ::=
SET DATABASE TRANSACTION CONTROL { LOCKS | MVLOCKS | MVCC
}</code>
</p>
<p>Set the concurrency control system for the database. It can be
issued only when all sessions have been committed or rolled back. This
command and its modes is discussed in the <a class="link" href="sessions-chapt.html" title="Chapter 3. Sessions and Transactions">Sessions and Transactions</a> chapter.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.tx</code>.</p>
<a name="N14B90" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE TRANSACTION ROLLBACK ON
CONFLICT</strong></span>
</p>
<p>
<span class="emphasis"><em>set database transaction rollback on conflict
statement</em></span>
</p>
<p>
<code class="literal"><set database transaction rollback on conflict
statement> ::= SET DATABASE TRANSACTION ROLLBACK ON CONFLICT { TRUE |
FALSE }</code>
</p>
<p>When a transaction deadlock or conflict is about to happen, the
current transaction is rolled back and an exception is raised. When this
property is set false, the transaction is not rolled back. Only the
latest statement that would cause the conflict is undone and an
exception is raised. The property should not be changed unless the
application can quickly perform an alternative statement and complete
the transaction. It is provided for compatibility with other database
engines which do not roll back the transaction upon deadlock. This
command is also discussed in the <a class="link" href="sessions-chapt.html" title="Chapter 3. Sessions and Transactions">Sessions and Transactions</a> chapter.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.tx_conflict_rollback</code>.</p>
<a name="N14BAC" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE DEFAULT ISOLATION
LEVEL</strong></span>
</p>
<p>
<span class="emphasis"><em>set database default isolation level
statement</em></span><code class="literal"> </code>
</p>
<p>
<code class="literal"><set database default isolation level> ::= SET
DATABASE DEFAULT ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE
}</code>
</p>
<p>Sets the transaction isolation level for new sessions. The
default is READ COMMITTED. Each session can also set its isolation
level.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.tx_level</code>.</p>
<a name="N14BC6" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE UNIQUE
NAME</strong></span>
</p>
<p>
<span class="emphasis"><em>set database unique name</em></span><code class="literal">
</code>
</p>
<p>
<code class="literal"><set database unique name statement> ::= SET
DATABASE UNIQUE NAME <identifier></code>
</p>
<p>Each HyperSQL catalog (database) has an engine-generated
internal name. This name is a 16 character long string, beginning with
HSQLDB and based on the time of creation of the database. The name is
used for the log events that are sent to external logging frameworks.
The new name must be exactly 16 characters long with no
spaces.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
</div>
<div class="section" title="SQL Conformance Settings">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_sql_settings"></a>SQL Conformance Settings</h3>
</div>
</div>
</div>
<p>These statements modify the level of conformance to the SQL
Standard in different areas. The settings that specify SQL SYNTAX are
for compatibility with other database engines and are FALSE by default.
For all the rest of the settings, TRUE means better conformance to the
Standard (unless the Standard defines the behaviour as implementation
dependent). The default value of a few of these settings is FALSE, due
to widespread non-conforming statements that are already in use in user
applications or statements generated by object relational tools. So long
as it is practical, it is best to set the non-conforming defaults to
TRUE in order to improve the quality of the database
application.</p>
<a name="N14BE1" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL RESTRICT
EXEC</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql restrict exec
statement</em></span>
</p>
<p>
<code class="literal"><set database sql restrict exec statement> ::=
SET DATABASE SQL RESTRICT EXEC { TRUE | FALSE }</code>
</p>
<p>Restricts or allows execution of SQL commands consisting of
multiple statements in a single string. The property also disallows or
allows the use of
<code class="methodname">java.sql.Statement.executeQuery()</code> for any DDL
or DML statement.</p>
<p>This property is <code class="literal">FALSE</code> by default. SQL
Standard and JDBC require restriction to a single statement. It is
advisable to restrict execution.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.restrict_exec</code>.</p>
<a name="N14C01" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL
SIZE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql size statement</em></span>
</p>
<p>
<code class="literal"><set database sql size statement> ::= SET
DATABASE SQL SIZE { TRUE | FALSE }</code>
</p>
<p>Enable or disable enforcement of column sizes for CHAR and
VARCHAR columns. The default is TRUE, meaning table definition must
contain <code class="literal">VARCHAR(n)</code> instead of
<code class="literal">VARCHAR</code>.</p>
<p>SQL Standard requires enforcement.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_size</code>.</p>
<a name="N14C21" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL
NAMES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql names statement</em></span>
</p>
<p>
<code class="literal"><set database sql names statement> ::= SET
DATABASE SQL NAMES { TRUE | FALSE }</code>
</p>
<p>Enable or disable full enforcement of the rule that prevents
SQL keywords being used for database object names such as columns and
tables. The default is <code class="literal">FALSE</code>, meaning
disabled.</p>
<p>SQL Standard requires enforcement. <span class="emphasis"><em>It is better to
enable this check, in order to improve the quality and correctness of
SQL statements.</em></span>
</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_names</code>.</p>
<a name="N14C40" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL REGULAR
NAMES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql regular names
statement</em></span>
</p>
<p>
<code class="literal"><set database sql regular names statement> ::=
SET DATABASE SQL REGULAR NAMES { TRUE | FALSE }</code>
</p>
<p>Enable or disable use of the underscore character at the
beginning, or the dollar character anywhere in database object names
such as columns and tables. The default is <code class="literal">TRUE</code>,
meaning disabled.</p>
<p>SQL Standard does not allow the underscore character at the
start of names, and does not allow the dollar character anywhere in a
name. This setting can be changed for compatibility with existing
database or for porting databases which include names that do not
conform to the Standard.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.regular_names</code>.</p>
<a name="N14C5D" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL
REFERENCES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql references
statement</em></span>
</p>
<p>
<code class="literal"><set database sql references statement> ::= SET
DATABASE SQL REFERENCES { TRUE | FALSE }</code>
</p>
<p>This command can enable or disable full enforcement of the rule
that prevents ambiguous column references in SQL statements (usually
SELECT statements). A column reference is ambiguous when it is not
qualified by a table name or table alias and can refer to more than one
column in a JOIN list.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>SQL Standard requires enforcement. <span class="emphasis"><em>It is better to
enable this check, in order to improve the quality and correctness of
SQL statements.</em></span> When false, the first matching table is used
to resolve the column reference.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_refs</code>.</p>
<a name="N14C7F" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL
TYPES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql types statement</em></span>
</p>
<p>
<code class="literal"><set database sql types statement> ::= SET
DATABASE SQL TYPES { TRUE | FALSE }</code>
</p>
<p>This command can enable or disable full enforcement of the
rules that prevents illegal type conversions and parameters or nulls
without type in SQL statements (usually SELECT statements). For example
an INTEGER column or a DATE column cannot be compared to a character
string or searched with a LIKE expression when the property is
<code class="literal">TRUE</code>.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>SQL Standard requires enforcement. <span class="emphasis"><em>It is better to
enable this check, in order to improve the quality and correctness of
SQL statements.</em></span>
</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_type</code>.</p>
<a name="N14CA3" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL TDC
DELETE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql tdc delete
statement</em></span>
</p>
<p>
<code class="literal"><set database sql tdc delete statement> ::= SET
DATABASE SQL TDC DELETE { TRUE | FALSE }</code>
</p>
<p>This command can enable or disable full enforcement of the SQL
Standard rules that prevents triggered data change exceptions caused by
ON DELETE CASCADE clauses of foreign key constraint.</p>
<p>When there are multiple constraints, a row may be updated by
one constraint and deleted by another constraint in the same operation.
This is not allowed by default. Changing this to false allows such
violations of the Standard to pass without an exception.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>SQL Standard requires enforcement, therefore this property
shouldn't be changed unless an application written for a non-conforming
RDBMS needs it.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_tdc_delete</code>.</p>
<a name="N14CC4" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL TDC
UPDATE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql tdc update
statement</em></span>
</p>
<p>
<code class="literal"><set database sql tdc update statement> ::= SET
DATABASE SQL TDC UPDATE { TRUE | FALSE }</code>
</p>
<p>This command can enable or disable full enforcement of the SQL
Standard rules that prevents triggered data change exceptions caused by
multiple ON UPDATE or ON DELETE SET clauses of foreign key constraint.
When there are multiple constraints, a field in a row may be updated by
two constraints to different values in the same operation. This is not
allowed by default. Changing this to <code class="literal">FALSE</code> allows
such violations of the Standard to pass without an exception.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>SQL Standard requires enforcement, therefore this property
shouldn't be changed unless an application written for a non-conforming
RDBMS needs it.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.enforce_tdc_update</code>.</p>
<a name="N14CE6" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL TRANSLATE TTI
TYPES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql translate tti types
statement</em></span>
</p>
<p>
<code class="literal"><set database sql translate tti types statement>
::= SET DATABASE SQL TRANSLATE TTI TYPES { TRUE | FALSE
}</code>
</p>
<p>The JDBC Specification up to version 4.1 does not support some
SQL Standard built-in types, therefore these types must be translated to
a supported type when accessed through JDBC ResultSet and
PreparedStatement methods.</p>
<p>If the property is true, the TIME / TIMESTAMP WITH TIME ZONE
types and INTERVAL types are represented in JDBC methods of
<code class="classname">ResultSetMetaData</code> and
<code class="classname">DatabaseMetaData</code> as JDBC datetime types without
time zone and the VARCHAR type respectively. The original type names are
preserved.</p>
<p>The property is <code class="literal">TRUE</code> by default. If set to
<code class="literal">FALSE</code>, the type codes for WITH TIME ZONE types will
be SQL type codes as opposed to JDBC type codes.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">jdbc.translate_tti_types</code>.</p>
<a name="N14D0E" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL CHARACTER
LITERAL</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql character
literal</em></span>
</p>
<p>
<code class="literal"><set database sql character literal statement>
::= SET DATABASE SQL CHARACTER LITERAL { TRUE | FALSE
}</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, the data type of
character literal strings is <code class="literal">CHARACTER</code>. When the
property is <code class="literal">FALSE</code> the data type is
<code class="literal">VARCHAR</code>.</p>
<p>Setting this property <code class="literal">FALSE</code> results in
strings not padded with spaces in <code class="literal">CASE WHEN</code>
expressions that have multiple literal alternatives.</p>
<p>SQL Standard requires the <code class="literal">CHARACTER</code>
type.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.char_literal</code>.</p>
<a name="N14D44" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL CONCAT
NULLS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql concat nulls
statement</em></span>
</p>
<p>
<code class="literal"><set database sql concat nulls statement> ::=
SET DATABASE SQL CONCAT NULLS { TRUE | FALSE }</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, concatenation of
a null value with a not-null value results in a null value. When the
property is <code class="literal">FALSE</code> this type of concatenation result
in the not-null value.</p>
<p>Setting this property <code class="literal">FALSE</code> results in
concatenation behaviour similar to Oracle or MS SQL Server.</p>
<p>SQL Standard requires a NULL result.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.concat_nulls</code>.</p>
<a name="N14D6E" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL UNIQUE
NULLS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql unique nulls
statement</em></span>
</p>
<p>
<code class="literal"><set database sql unique nulls statement> ::=
SET DATABASE SQL UNIQUE NULLS { TRUE | FALSE }</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, with multi-column
UNIQUE constraints, it is possible to insert multiple rows for which one
or more of the values for the constraint columns is NULL. When the
property is <code class="literal">FALSE</code>, if there is any not-null value in
the columns, then the set of values is compared to the existing rows and
if there is a match, an exception is thrown. The setting
<code class="literal">FALSE</code>, makes the behaviour more restrictive. For
example, inserting (1, null) twice is possible by default, but not
possible when the property is <code class="literal">FALSE</code>.</p>
<p>Setting this property <code class="literal">FALSE</code> results in
UNIQUE constraint behaviour similar to Oracle.</p>
<p>SQL Standard requires the default (TRUE) behaviour.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.unique_nulls</code>.</p>
<a name="N14D9E" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL CONVERT
TRUNCATE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql convert
truncate</em></span>
</p>
<p>
<code class="literal"><set database sql convert truncate statement>
::= SET DATABASE SQL CONVERT TRUNCATE { TRUE | FALSE
}</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, conversion from a
floating point value (a DOUBLE value) to an integral type always
truncates the fractional part. When the property is
<code class="literal">FALSE</code>, rounding takes place instead of truncation.
For example, assigning the value 123456E-2 to an integer column will
result in 1234 by default, but 1235 when the property is
<code class="literal">FALSE</code>.</p>
<p>Standard SQL considers this behaviour implementation
dependent.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.convert_trunc</code>.</p>
<a name="N14DC6" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL AVG
SCALE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql avg scale</em></span>
</p>
<p>
<code class="literal"><set database sql avg scale> ::= SET DATABASE
SQL AVG SCALE <numeric value></code>
</p>
<p>By default, the result of division and the AVG and MEDIAN
aggregate functions has the same type as the aggregated type of the
values. This includes the scale. The scale specified with this property
is used if it is larger than the scale of the operation. For example,
the average of 5 and 10 is 7 by default, but 7.50 if the scale is
specified as 2. The result of 7/3 is 2 by default but 2.33 if the scale
is specified as 2.</p>
<p>Standard SQL considers this behaviour implementation dependent.
Some databases use a default scale larger than zero.</p>
<p>The property is <code class="literal">0</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.avg_scale</code>.</p>
<a name="N14DE5" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL DOUBLE
NAN</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql double nan</em></span>
</p>
<p>
<code class="literal"><set database sql double nan> ::= SET DATABASE
SQL DOUBLE NAN { TRUE | FALSE }</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, division of a
floating point value (a DOUBLE value) by zero raises an exception. When
the property is <code class="literal">FALSE</code>, a Java
<code class="literal">Double.NaN</code>, <code class="literal">POSITIVE_INFINITY</code> or
<code class="literal">NEGATIVE_INFINITY</code> value is returned.</p>
<p>Standard SQL requires an exception to be raised.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.double_nan</code>.</p>
<a name="N14E13" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL NULLS
FIRST</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql nulls first</em></span>
</p>
<p>
<code class="literal"><set database sql nulls first> ::= SET DATABASE
SQL NULLS FIRST { TRUE | FALSE }</code>
</p>
<p>When the property is <code class="literal">TRUE</code>, nulls appear
before values in result sets with ORDER BY. When set FALSE, nulls appear
after the values. Some databases, including PostgreSQL, Oracle and MS
SQL Server, return nulls after the values.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.nulls_first</code>.</p>
<a name="N14E33" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL NULLS
ORDER</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql nulls order</em></span>
</p>
<p>
<code class="literal"><set database sql nulls order> ::= SET DATABASE
SQL NULLS ORDER { TRUE | FALSE }</code>
</p>
<p>When NULLS FIRST or NULLS LAST is used explicitly in the ORDER
BY clause, this property is ignored.</p>
<p>When the property is <code class="literal">TRUE</code>, nulls appear
according to the value of NULL FIRST property as described
above.</p>
<p>When set <code class="literal">FALSE</code>, nulls appear according to
the value of NULLS FIRST property when DESC is not used in the ORDER BY
clause. But if DESC is used, the position of nulls is reversed. Some
databases, including MySQL and Oracle, return nulls in this manner when
DESC is used in ORDER BY.</p>
<p>The property is <code class="literal">TRUE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.nulls_order</code>.</p>
<a name="N14E5A" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL
IGNORECASE</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql ignorecase</em></span>
</p>
<p>
<code class="literal"><set database sql ignorecase> ::= SET DATABASE
SQL IGNORECASE { TRUE | FALSE }</code>
</p>
<p>This property is <code class="literal">FALSE</code> by default and should
only be used in special circumstances where compatibility with a
different database is required.</p>
<p>When the property is <code class="literal">TRUE</code>, all declarations
of <code class="literal">VARCHAR</code> columns in tables or other database
objects are converted to <code class="literal">VARCHAR_IGNORECASE</code>. This has
a global effect on the database, unlike the <code class="literal">SET
IGNORECASE</code> statement which applies only to the current
session.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.ignore_case</code>.</p>
<a name="N14E88" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL LIVE
OBJECT</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql live object</em></span>
</p>
<p>
<code class="literal"><set database sql live object> ::= SET DATABASE
SQL LIVE OBJECT { TRUE | FALSE }</code>
</p>
<p>This property is <code class="literal">FALSE</code> by default and can
only be used in <code class="literal">mem:</code> databases.</p>
<p>When the property is <code class="literal">FALSE</code>, all java objects
stored in a column of type <code class="literal">OTHER</code> are serialized. When
the property is <code class="literal">FALSE</code>, objects are not serialized at
all.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.live_object</code>.</p>
<a name="N14EAF" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYS INDEX
NAMES</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql sys index names</em></span>
</p>
<p>
<code class="literal"><set database sql sys table names statement> ::=
SET DATABASE SQL SYS INDEX NAMES { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, changes the naming method for
system generated indexes that are used to back constraints. By default,
the names of those indexes are generated as strings with SYS_ prefixes.
When the property is set TRUE, the names will be the same as the
constraint names.</p>
<p>Changing the property does not affect the names of indexes for
tha constraints that have already been defined. After a restart of the
database all system-generated indexes are named according to the setting
for this property.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.sys_index_names</code>.</p>
<a name="N14ECE" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYNTAX
DB2</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql syntax DB2</em></span>
</p>
<p>
<code class="literal"><set database sql syntax DB2 statement> ::= SET
DATABASE SQL SYNTAX DB2 { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, enables support for some elements
of DB2 syntax. Single-row SELECT statements (<code class="literal">SELECT
<expression list></code> without the FROM clause) are supported
and treated as the SQL Standard equivalent, <code class="literal">VALUES
<expression list></code>. The DUAL table is supported, as well
as the ROWNUM pseudo-column. BINARY type definitions such as VARCHAR(L)
FOR BIT DATA are supported. Empty DEFAULT clauses in column definitions
are supported.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.syntax_db2</code>.</p>
<a name="N14EF1" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYNTAX
MSS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql syntax MSS</em></span>
</p>
<p>
<code class="literal"><set database sql syntax MSS statement> ::= SET
DATABASE SQL SYNTAX MSS { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, enables support for some elements
of SQLServer syntax. Single-row SELECT statements (<code class="literal">SELECT
<expression list></code> without the FROM clause) are supported
and treated as the SQL Standard equivalent, <code class="literal">VALUES
<expression list></code>. The parameters of CONVERT() function
are switched in this mode.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.syntax_mss</code>.</p>
<a name="N14F14" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYNTAX
MYS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql syntax MYS</em></span>
</p>
<p>
<code class="literal"><set database sql syntax MYS statement> ::= SET
DATABASE SQL SYNTAX MYS { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, enables support for some elements
of MySQL syntax. The TEXT data type is translated to
LONGVARCHAR.</p>
<p>In CREATE TABLE statements, [NOT NULL | NULL] can be used
immediately after the column type name and before the DEFAULT clause.
AUTO_INCREMENT is translated to the GENERATED BY DEFAULT AS IDENTITY
clause.</p>
<p>Single-row SELECT statements (<code class="literal">SELECT <expression
list></code> without the FROM clause) are supported and treated as
the SQL Standard equivalent, <code class="literal">VALUES <expression
list></code>.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.syntax_mys</code>.</p>
<a name="N14F3B" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYNTAX
ORA</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql syntax ORA</em></span>
</p>
<p>
<code class="literal"><set database sql syntax ORA statement> ::= SET
DATABASE SQL SYNTAX ORA { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, enables support for some elements
of Oracle syntax. The DUAL table is supported, together with ROWNUM,
NEXTVAL and CURRVAL syntax and semantics.</p>
<p>The non-standard types are translated to supported standard
types. BINARY_DOUBLE and BINARY_FLOAT are translated to DOUBLE. LONG RAW
and RAW are translated to VARBINARY with long or medium length limits.
LONG and VARCHAR2 are translated to VARCHAR with long or medium length
limits. NUMBER is translated to DECIMAL. Some extra type conversions and
no-arg functions are also allowed in this mode.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.syntax_ora</code>.</p>
<a name="N14F5A" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE SQL SYNTAX
PGS</strong></span>
</p>
<p>
<span class="emphasis"><em>set database sql syntax PGS</em></span>
</p>
<p>
<code class="literal"><set database sql syntax PGS statement> ::= SET
DATABASE SQL SYNTAX PGS { TRUE | FALSE }</code>
</p>
<p>This property, when set TRUE, enables support for some elements
of PosgtreSQL syntax. The TEXT data type is translated to LONGVARCHAR,
while the SERIAL data types is translated to BIGINT together with
GENERATED BY DEFAULT AS IDENTITY.</p>
<p>Single-row SELECT statements (<code class="literal">SELECT <expression
list></code> without the FROM clause) are supported and treated as
the SQL Standard equivalent, <code class="literal">VALUES <expression
list></code>.</p>
<p>The functions <code class="literal">NEXTVAL(<sequence name
string>)</code>, <code class="literal">CURRVAL(<sequence name
string>)</code> and <code class="literal">LASTVAL()</code> are supported in
this compatibility mode.</p>
<p>The property is <code class="literal">FALSE</code> by default.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">sql.syntax_pgs</code>.</p>
<a name="N14F8A" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE REFERENTIAL
INTEGRITY</strong></span>
</p>
<p>
<span class="emphasis"><em>set database referential integrity
statement</em></span>
</p>
<p>
<code class="literal"><set database referential integrity statement>
::= SET DATABASE REFERENTIAL INTEGRITY { TRUE | FALSE
}</code>
</p>
<p>This command enables or disables the enforcement of referential
integrity constraints (foreign key constraints), check constraints apart
from NOT NULL and execution of triggers. By default, all constraints are
checked.</p>
<p>The only legitimate use of this statement is before importing
large amounts of external data into tables that have existing FOREIGN
KEY constraints. After import, the statement must be used again to
enable constraint enforcement.</p>
<p>If you are not sure the data conforms to the constraints, run
queries to verify all rows conform to the FOREIGN KEY constraints and
take appropriate actions for the rows that do not conform.</p>
<p>A query example to return the rows in a foreign key table that
have no parent is given below:</p>
<div class="example">
<a name="N14FA1"></a>
<p class="title">
<b>Example 11.7. Finding foreign key rows with no parents after a bulk
import</b>
</p>
<div class="example-contents">
<pre class="screen"> SELECT * FROM foreign_key_table LEFT OUTER JOIN primary_key_table
ON foreign_key_table.fk_col = primary_key_table.pk_col WHERE primary_key_table.pk_col IS NULL</pre>
</div>
</div>
<br class="example-break">
<p>Only a user with the DBA role can execute this
statement.</p>
</div>
<div class="section" title="Cache, Persistence and Files Settings">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_cache_persistence"></a>Cache, Persistence and Files Settings</h3>
</div>
</div>
</div>
<p>These statements control the memory and other settings for
database persistence.</p>
<a name="N14FAE" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES BACKUP INCREMENT
</strong></span>
</p>
<p>
<span class="emphasis"><em>set files backup increment
statement</em></span>
</p>
<p>
<code class="literal"><set files backup increment statement> ::= SET
FILES BACKUP INCREMENT { TRUE | FALSE }</code>
</p>
<p>Older versions of HSQLDB perform a backup of the .data file
before its contents are modified and the whole .data file is saved in a
compressed form when a CHECKPOINT or SHUTDOWN is performed. This takes a
long time when the size of the database exceeds 100 MB or so (on an
average 2010 computer, you can expect a backup speed of 20MB per second
or more).</p>
<p>The alternative is backup in increments, just before some part
of the .data file is modified. In this mode, no backup is performed at
CHECKPOINT or SHUTDOWN. This mode is preferred for large databases which
are opened and closed frequently.</p>
<p>The default mode is <code class="literal">TRUE</code>. If the old method
of backup is preferred, the mode can be set
<code class="literal">FALSE</code>.</p>
<p>Warning: The old, non-incremental setting, FALSE, shouldn't be
used at all when the data file is larger than 4GB. If it is used, the
data file is not fully backed up and can result in corruption. The zip
compression method is used in this mode and it is limited to 4GB
size.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.inc_backup</code>.</p>
<a name="N14FD2" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES CACHE ROWS</strong></span>
</p>
<p>
<span class="emphasis"><em>set files cache rows statement</em></span><code class="literal">
</code>
</p>
<p>
<code class="literal"><set files cache rows statement> ::= SET FILES
CACHE ROWS <unsigned integer literal></code>
</p>
<p>Sets the maximum number of rows (of CACHED tables) held in the
memory cache. The default is 50000 rows.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.cache_rows</code>.</p>
<a name="N14FEC" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES CACHE SIZE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files cache size statement</em></span><code class="literal">
</code>
</p>
<p>
<code class="literal"><set files cache size statement> ::= SET FILES
CACHE SIZE <unsigned integer literal></code>
</p>
<p>Sets maximum amount of data (of CACHED tables) in kilobytes
held in the memory cache. The default is 10000 kilobytes. Note the
amount of memory used is larger than this amount, which does not account
for Java object size overheads.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.cache_size</code>.</p>
<a name="N15006" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES DEFRAG</strong></span>
</p>
<p>
<span class="emphasis"><em>set files defrag statement</em></span>
</p>
<p>
<code class="literal"><set files defrag statement> ::= SET FILES
DEFRAG <unsigned integer literal></code>
</p>
<p>Sets the threshold for performing a DEFRAG during a checkpoint.
The <code class="literal"><unsigned integer literal></code> is the
percentage of abandoned space in the <code class="literal">*.data</code> file.
When a CHECKPOINT is performed either as a result of the
<code class="literal">.log</code> file reaching the limit set by <code class="literal">SET
FILES LOG SIZE m</code>, or by the user issuing a CHECKPOINT command,
the amount of space abandoned since the database was opened is checked
and if it is larger than the specified percentage, a CHECKPOINT DEFRAG
is performed instead of a CHECKPOINT. As the DEFRAG operation uses a lot
of memory and takes a long time with large databases, setting the
threshold well above zero is suitable for databases that are around than
500 MB or more.</p>
<p>The default is 0, which indicates no DEFRAG. Useful values are
between 30 to 60.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.defrag_limit</code>.</p>
<a name="N1502C" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES LOG</strong></span>
</p>
<p>
<span class="emphasis"><em>set files log statement</em></span>
</p>
<p>
<code class="literal"><set files log statement> ::= SET FILES LOG {
TRUE | FALSE }</code>
</p>
<p>Sets logging of database operations on or off. Turning logging
off is for special usage, such as temporary cache usage. The default is
TRUE.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.log_data</code>.</p>
<a name="N15044" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES LOG SIZE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files log size statement</em></span>
</p>
<p>
<code class="literal"><set files log size statement> ::= SET FILES LOG
SIZE <unsigned integer literal></code>
</p>
<p>Sets the maximum size in MB of the <code class="literal">*.log</code>
file to the specified value. The default maximum size is 50 MB. If the
value is zero, no limit is used for the size of the file. When the size
of the file reaches this value, a CHECKPOINT is performed and the the
<code class="literal">*.log</code> file is cleared to size 0.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.log_size</code>.</p>
<a name="N15062" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES NIO</strong></span>
</p>
<p>
<span class="emphasis"><em>set files nio</em></span>
</p>
<p>
<code class="literal"><set files nio statement> ::= SET FILES NIO {
TRUE | FALSE }</code>
</p>
<p>Sets the access method of the .data file. The default is TRUE
and uses the Java nio classes to access the file via memory-mapped
buffers.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.nio_data_file</code>.</p>
<a name="N1507A" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES NIO SIZE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files nio size</em></span>
</p>
<p>
<code class="literal"><set files nio size statement> ::= SET FILES NIO
SIZE <unsigned integer literal></code>
</p>
<p>Sets The maximum size of .data file in megabytes that can use
the nio access method. When the file gets larger than this limit,
non-nio access methods are used. Values 64, 128, 256, 512, 1024 and
larger multiples of 512 can be used. The default is 256MB.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.nio_max_size</code>.</p>
<a name="N15092" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES WRITE
DELAY</strong></span>
</p>
<p>
<span class="emphasis"><em>set files write delay statement</em></span>
</p>
<p>
<code class="literal"><set files write delay statement> ::= SET FILES
WRITE DELAY {{ TRUE | FALSE } | <seconds value> | <milliseconds
value> MILLIS}</code>
</p>
<p>Set the WRITE DELAY property of the database. The WRITE DELAY
controls the frequency of file sync for the log file. When WRITE_DELAY
is set to FALSE or 0, the sync takes place immediately at each COMMIT.
WRITE DELAY TRUE performs the sync once every 0.5 seconds (which is the
default). A numeric value can be specified instead.</p>
<p>The purpose of this command is to control the amount of data loss
in case of a total system crash. A delay of 1 second means at most the
data written to disk during the last second before the crash is lost.
All data written prior to this has been synced and should be
recoverable.</p>
<p>A write delay of 0 impacts performance in high load situations, as
the engine has to wait for the file system to catch up.</p>
<p>To avoid this, you can set write delay down to 10
milliseconds.</p>
<p>Each time the SET FILES WRITE DELAY statement is executed with any
value, a sync is immediately performed.</p>
<p>Only a user with the DBA role can execute this statement.</p>
<p>This is equivalent to the connection properties
<code class="literal">hsqldb.write_delay</code> and
<code class="literal">hsqldb.write_delay_millis</code>.</p>
<a name="N150B5" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES SCALE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files scale</em></span>
</p>
<p>
<code class="literal"><set files scale statement> ::= SET FILES SCALE
<scale value></code>
</p>
<p>Changes the scale factor for the .data file. The default scale
is 32 and allows 64GB of data storage capacity. The scale can be
increased in order to increase the maximum data storage capacity. The
scale values 8, 16, 32, 64, 128, 256, 512, 1024 are allowed. Scale value
1024 allows a maximum capacity of 2 TB.</p>
<p>This command can be used only when there is no data in CACHED
tables. This is equivalent to the connection property
<code class="literal">hsqldb.cache_file_scale</code>.</p>
<p>The scale factor indicates the size of the unit of storage of
data in bytes. For example, with a scale factor of 128, a row containing
a small amount of data will use 128 bytes. Larger rows may use multiple
units of 128 bytes.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.cache_file_scale</code>.</p>
<a name="N150D4" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES LOB SCALE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files lob scale</em></span>
</p>
<p>
<code class="literal"><set files lob scale statement> ::= SET FILES
LOB SCALE <scale value></code>
</p>
<p>Changes the scale factor for the .lobs file. The scale is
interpreted in kilobytes. The default scale is 32 and allows 64TB of lob
data storage capacity. The scale can be reduced in order to improve
storage efficiency. If the lobs are a lot smaller than 32 kilobytes,
reducing the scale will reduce wasted space. The scale values 1, 2, 4,
8, 16, 32 are allowed. For example if the average size of lobs is 4
kilobytes, the default scale of 32 will result in 28KB wasted space for
each lob. Reducing the lob scale to 2 will result in average 1KB wasted
space for each lob.</p>
<p>This command can be used only when there is no lob in the
database.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.lob_file_scale</code>.</p>
<a name="N150EE" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES LOB
COMPRESSED</strong></span>
</p>
<p>
<span class="emphasis"><em>set files lob compressed</em></span>
</p>
<p>
<code class="literal"><set files lob compressed statement> ::= SET
FILES LOB COMPRESSED { TRUE | FALSE }</code>
</p>
<p>By default, lobs are not compressed for storage. When this
setting is <code class="literal">TRUE</code>, all BLOB and CLOB values stored in
the database are compressed. Compression reduces the storage size but
increases the access time.</p>
<p>This command can be used only when there is no lob in the
database.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>This is equivalent to the connection property
<code class="literal">hsqldb.lob_compressed</code>.</p>
<a name="N1510B" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES SCRIPT
FORMAT</strong></span>
</p>
<p>
<span class="emphasis"><em>set files script format</em></span>
</p>
<p>
<code class="literal"><set files script format statement> ::= SET
FILES SCRIPT FORMAT { TEXT | COMPRESSED }</code>
</p>
<p>Changes the compression setting for database scripts. The
default is text. Using COMPRESSED results in the storage of the .script
file in gzip compressed form. Using this command causes a
CHECKPOINT.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N1511E" class="indexterm"></a>
<p>
<span class="bold"><strong>SET FILES SPACE</strong></span>
</p>
<p>
<span class="emphasis"><em>set files space</em></span>
</p>
<p>
<code class="literal"><set files space statement> ::= SET FILES SPACE
TRUE</code>
</p>
<p>Enables use of table spaces for CACHED tables. Each table is
allocated space in blocks. The size of each block in mega bytes is equal
to the data file scale divided by 16. The default data file scale is 32
so the default size of each block is 2 MB. See the SET TABLE NEW SPACE
statement below.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N15131" class="indexterm"></a>
<p>
<span class="bold"><strong>SET TABLE NEW SPACE</strong></span>
</p>
<p>
<span class="emphasis"><em>set table new space</em></span>
</p>
<p>
<code class="literal"><set table new space statement> ::= SET TABLE
<table name> NEW SPACE</code>
</p>
<p>Sets the named table to use it's own space blocks within the
.data file. Use of table spaces should be enabled with the SET FILES
SPACE statement above, before this statement is executed.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<a name="N15144" class="indexterm"></a>
<p>
<span class="bold"><strong>SET TABLE TYPE</strong></span>
</p>
<p>
<span class="emphasis"><em>set table type</em></span>
</p>
<p>
<code class="literal"><set table type statement> ::= SET TABLE
<table name> TYPE { MEMORY | CACHED }</code>
</p>
<p>Changes the storage type of an existing table between CACHED
and MEMORY types.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
</div>
<div class="section" title="Authentication Settings">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="mtc_authntication_settings"></a>Authentication Settings</h3>
</div>
</div>
</div>
<p>Two settings are available for authentication control.</p>
<p>When the default password authentication is used, the passwords
can be checked for complexity according to administrative rules</p>
<a name="N1515F" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE PASSWORD CHECK
FUNCTION</strong></span>
</p>
<p>
<span class="emphasis"><em>set database password check
function</em></span>
</p>
<p>
<code class="literal"><set database password check function statement>
::= SET DATABASE PASSWORD CHECK FUNCTION { <routine body> | NONE
}</code>
</p>
<p>The routine body is the body of a function that has a VARCHAR
parameter and returns a BOOLEAN. This function checks the
<code class="literal">PASSWORD</code> submitted as parameter and returns TRUE if
it conforms to complexity checks, or FALSE, if it does not.</p>
<p>The <code class="literal"><routine body></code> can be an SQL block
or an external Java function reference. This is covered in the <a class="link" href="sqlroutines-chapt.html" title="Chapter 8. SQL-Invoked Routines">SQL-Invoked Routines</a>
chapter</p>
<p>To disable this mechanism, the token <code class="literal">NONE</code>
can be specified instead of the <code class="literal"><routine
body></code>.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<p>In the examples below, an SQL function and a Java function are
used.</p>
<pre class="programlisting"> SET DATABASE PASSWORD CHECK FUNCTION
BEGIN ATOMIC
IF CHAR_LENGTH(PASSWORD) > 6 THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END IF;
END
SET DATABASE PASSWORD CHECK FUNCTION EXTERNAL NAME 'CLASSPATH:org.anorg.access.AccessClass.accessMethod'
// the Java method is defined like this
public static boolean accessMethod(String param) {
return param != null && param.length > 6;
}
</pre>
<p>It is possible to replace the default password authentication
completely with a function that uses external authentication servers,
such as LDAP. This function is called each time a user connects to the
database.</p>
<a name="N1518C" class="indexterm"></a>
<p>
<span class="bold"><strong>SET DATABASE AUTHENTICATION
FUNCTION</strong></span>
</p>
<p>
<span class="emphasis"><em>set database authentication
function</em></span>
</p>
<p>
<code class="literal"><set database authentication function statement>
::= SET DATABASE AUTHENTICATION FUNCTION { <external body
reference> | NONE }</code>
</p>
<p>The routine body is an external Java function reference. This
function has three String parameters. The first parameter is the unique
name of the database, the second parameter the user name, and the third
parameter the password.</p>
<p>External authentication can be used in two different patterns.
In the first pattern, user names must be stored in the database. In the
second pattern, user names shouldn't be stored in the database and any
names that are stored in the database are ignored.</p>
<p>In both patterns, the username and password are checked by the
authentication function. If the function throws a runtime exception then
authentication fails.</p>
<p>In the first pattern, the function always returns null if
authentication is successful.</p>
<p>In the second pattern, the function returns a list of role
names that have been granted to the user. These roles must match the
ROLE objects that have been defined in the database.</p>
<p>The Java function should return an instance of
org.hsqldb.jdbc.JDBCArrayBasic constructed with a String[] argument that
contains the role names.</p>
<p>Only a user with the DBA role can execute this
statement.</p>
<pre class="programlisting"> SET DATABASE AUTHENTICATION FUNCTION EXTERNAL NAME 'CLASSPATH:org.anorg.access.AccessClass.accessExernalMethod'
// the Java method is defined like this
public static java.sql.Array accessExternalMethod(String database, String user, String password) {
if (externalCheck(database, user, password) {
return null;
}
throw new RuntimeException("failed to authenticate");
}
</pre>
</div>
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