<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>berkdb open</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB TCL API Reference" /> <link rel="up" href="tclapi.html" title="Chapter 1. Berkeley DB Tcl APIs" /> <link rel="prev" href="db_join.html" title="db join" /> <link rel="next" href="db_put.html" title="db put" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">berkdb open</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="db_join.html">Prev</a> </td> <th width="60%" align="center">Chapter 1. Berkeley DB Tcl APIs </th> <td width="20%" align="right"> <a accesskey="n" href="db_put.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="db_open"></a>berkdb open</h2> </div> </div> </div> <pre class="programlisting">berkdb open [-auto_commit] [-btree | -hash | -recno | -queue | -unknown] [-cachesize {gbytes bytes ncache}] [-create] [-delim delim] [-dup] [-dupsort] [-encrypt] [-encryptaes passwd] [-encryptany passwd] [-env env] [-errfile filename] [-excl] [-extent size] [-ffactor density] [-len len] [-mode mode] [-nelem size] [-pad pad] [-pagesize pagesize] [-rdonly] [-recnum] [-renumber] [-snapshot] [-source file] [-truncate] [-txn txnid] [--] [file [database]] </pre> <p> The <span class="bold"><strong>berkdb open</strong></span> command opens and optionally creates a database. The returned database handle is bound to a Tcl command of the form <span class="bold"><strong>dbN</strong></span>, where N is an integer starting at 0 (for example, db0 and db1). It is through this Tcl command that the script accesses the database methods. </p> <p> The options are as follows: </p> <div class="itemizedlist"> <ul type="disc"> <li> <p> <span class="bold"><strong>-auto_commit</strong></span> </p> <p> Enclose the call within an implicit transaction (you do not need to provide a transaction handle as a transaction is internally created and commited for you). If the call succeeds, the open operation will be recoverable and all subsequent database modification operations based on this handle will be transactionally protected. If the call fails, no database will have been created. </p> </li> <li> <p> <span class="bold"><strong>-btree</strong></span> </p> <p> Open/create a database of type Btree. The Btree format is a representation of a sorted, balanced tree structure. </p> </li> <li> <p> <span class="bold"><strong>-hash</strong></span> </p> <p> Open/create a database of type Hash. The Hash format is an extensible, dynamic hashing scheme. </p> </li> <li> <p> <span class="bold"><strong>-queue</strong></span> </p> <p> Open/create a database of type Queue. The Queue format supports fast access to fixed-length records accessed by sequentially or logical record number. </p> </li> <li> <p> <span class="bold"><strong>-recno</strong></span> </p> <p> Open/create a database of type Recno. The Recno format supports fixed- or variable-length records, accessed sequentially or by logical record number, and optionally retrieved from a flat text file. </p> </li> <li> <p> <span class="bold"><strong>-unknown</strong></span> </p> <p> The database is of an unknown type, and must already exist. </p> </li> <li> <p> <span class="bold"><strong>-cachesize {gbytes bytes ncache}</strong></span> </p> <p> Set the size of the database's shared memory buffer pool (that is, the cache), to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. The cache should be the size of the normal working data set of the application, with some small amount of additional memory for unusual situations. (Note: The working set is not the same as the number of simultaneously referenced pages, and should be quite a bit larger!) </p> <p> The default cache size is 256KB, and may not be specified as less than 20KB. Any cache size less than 500MB is automatically increased by 25% to account for buffer pool overhead; cache sizes larger than 500MB are used as specified. </p> <p> It is possible to specify caches to Berkeley DB that are large enough so that they cannot be allocated contiguously on some architectures; for example, some releases of Solaris limit the amount of memory that may be allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated contiguously in memory. If it is greater than 1, the cache will be broken up into <span class="bold"><strong>ncache</strong></span> equally sized separate pieces of memory. </p> <p> For information on tuning the Berkeley DB cache size, see <a href="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">Selecting a Cache Size</a> in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. </p> <p> Because databases opened within Berkeley DB environments use the cache specified to the environment, it is an error to attempt to set a cache in a database created within an environment. </p> </li> <li> <p> <span class="bold"><strong>-create</strong></span> </p> <p> Create any underlying files, as necessary. If the files do not already exist and the <span class="bold"><strong>-create</strong></span> argument is not specified, the call will fail. </p> </li> <li> <p> <span class="bold"><strong>-delim delim</strong></span> </p> <p> Set the delimiting byte used to mark the end of a record in the backing source file for the Recno access method. </p> <p> This byte is used for variable length records if the <span class="bold"><strong>-source</strong></span> argument file is specified. If the <span class="bold"><strong>-source</strong></span> argument file is specified and no delimiting byte was specified, <newline> characters (that is, ASCII 0x0a) are interpreted as end-of-record markers. </p> </li> <li> <p> <span class="bold"><strong>-dup</strong></span> </p> <p> Permit duplicate data items in the tree, that is, insertion when the key of the key/data pair being inserted already exists in the tree will be successful. The ordering of duplicates in the tree is determined by the order of insertion unless the ordering is otherwise specified by use of a cursor or a duplicate comparison function. </p> <p> It is an error to specify both <span class="bold"><strong>-dup</strong></span> and <span class="bold"><strong>-recnum</strong></span>. </p> </li> <li> <p> <span class="bold"><strong>-dupsort</strong></span> </p> <p> Sort duplicates within a set of data items. A default lexical comparison will be used. Specifying that duplicates are to be sorted changes the behavior of the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>put</strong></span> operation as well as the <span class="emphasis"><em>dbc</em></span> <span class="bold"><strong>put</strong></span> operation when the <span class="bold"><strong>-keyfirst</strong></span>, <span class="bold"><strong>-keylast</strong></span> and <span class="bold"><strong>-current</strong></span> options are specified. </p> </li> <li> <p> <span class="bold"><strong>-encrypt</strong></span> </p> <p> Specify the database in an environment should be encrypted with the same password that is being used in the environment. </p> </li> <li> <p> <span class="bold"><strong>-encryptaes passwd</strong></span> </p> <p> Specify the database should be encrypted with the given password using the Rijndael/AES (also known as the Advanced Encryption Standard and Federal Information Processing Standard (FIPS) 197) algorithm. </p> </li> <li> <p> <span class="bold"><strong>-encryptany passwd</strong></span> </p> <p> Specify the already existing database should be opened with the given password. This option is used if the database is known to be encrypted, but the specific algorithm used is not known. </p> </li> <li> <p> <span class="bold"><strong>-env env</strong></span> </p> <p> If no <span class="bold"><strong>-env</strong></span> argument is given, the database is standalone; that is, it is not part of any Berkeley DB environment. </p> <p> If a <span class="bold"><strong>-env</strong></span> argument is given, the database is created within the specified Berkeley DB environment. The database access methods automatically make calls to the other subsystems in Berkeley DB, based on the enclosing environment. For example, if the environment has been configured to use locking, the access methods will automatically acquire the correct locks when reading and writing pages of the database. </p> </li> <li> <p> <span class="bold"><strong>-errfile filename</strong></span> </p> <p> When an error occurs in the Berkeley DB library, a Berkeley DB error or an error return value is returned by the function. In some cases, however, the errno value may be insufficient to completely describe the cause of the error especially during initial application debugging. </p> <p> The <span class="bold"><strong>-errfile</strong></span> argument is used to enhance the mechanism for reporting error messages to the application by specifying a file to be used for displaying additional Berkeley DB error messages. In some cases, when an error occurs, Berkeley DB will output an additional error message to the specified file reference. </p> <p> The error message will consist of a Tcl command name and a colon (":"), an error string, and a trailing <newline> character. If the database was opened in an environment, the Tcl command name will be the environment name (for example, env0), otherwise it will be the database command name (for example, db0). </p> <p> This error-logging enhancement does not slow performance or significantly increase application size, and may be run during normal operation as well as during application debugging. </p> <p> For database handles opened inside of Berkeley DB environments, specifying the <span class="bold"><strong>-errfile</strong></span> argument affects the entire environment and is equivalent to specifying the same argument to the <span class="bold"><strong>berkdb env</strong></span> command. </p> </li> <li> <p> <span class="bold"><strong>-excl</strong></span> </p> <p> Return an error if the database already exists. </p> </li> <li> <p> <span class="bold"><strong>-extent size</strong></span> </p> <p> Set the size of the extents of the Queue database; the size is specified as the number of pages in an extent. Each extent is created as a separate physical file. If no extent size is set, the default behavior is to create only a single underlying database file. </p> <p> For information on tuning the extent size, see <a href="../../programmer_reference/rq_conf.html#am_conf_extentsize" class="olink">Selecting an Extent Size</a> in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. </p> </li> <li> <p> <span class="bold"><strong>-ffactor density</strong></span> </p> <p> Set the desired density within the hash table. </p> <p> The density is an approximation of the number of keys allowed to accumulate in any one bucket </p> </li> <li> <p> <span class="bold"><strong>-len len</strong></span> </p> <p> For the Queue access method, specify that the records are of length <span class="bold"><strong>len</strong></span>. </p> <p> For the Recno access method, specify that the records are fixed-length, not byte-delimited, and are of length <span class="bold"><strong>len</strong></span>. </p> <p> Any records added to the database that are less than <span class="bold"><strong>len</strong></span> bytes long are automatically padded (see the <span class="bold"><strong>-pad</strong></span> argument for more information). </p> <p> Any attempt to insert records into the database that are greater than <span class="bold"><strong>len</strong></span> bytes long will cause the call to fail immediately and return an error. </p> </li> <li> <p> <span class="bold"><strong>-mode mode</strong></span> </p> <p> On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by the access methods are created with mode <span class="bold"><strong>mode</strong></span> (as described in <span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). The group ownership of created files is based on the system and directory defaults, and is not further specified by Berkeley DB. If <span class="bold"><strong>mode</strong></span> is 0, files are created readable and writable by both owner and group. On Windows systems, the mode argument is ignored. </p> </li> <li> <p> <span class="bold"><strong>-nelem size</strong></span> </p> <p> Set an estimate of the final size of the hash table. </p> <p> If not set or set too low, hash tables will still expand gracefully as keys are entered, although a slight performance degradation may be noticed. </p> </li> <li> <p> <span class="bold"><strong>-pad pad</strong></span> </p> <p> Set the padding character for short, fixed-length records for the Queue and Recno access methods. </p> <p> If no pad character is specified, <space> characters (that is, ASCII 0x20) are used for padding. </p> </li> <li> <p> <span class="bold"><strong>-pagesize pagesize</strong></span> </p> <p> Set the size of the pages used to hold items in the database, in bytes. The minimum page size is 512 bytes, and the maximum page size is 64K bytes. If the page size is not explicitly set, one is selected based on the underlying filesystem I/O block size. The automatically selected size has a lower limit of 512 bytes and an upper limit of 16K bytes. </p> <p> For information on tuning the Berkeley DB page size, see <a href="../../programmer_reference/general_am_conf.html#am_conf_pagesize" class="olink">Selecting a Page Size</a> in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. </p> </li> <li> <p> <span class="bold"><strong>-rdonly</strong></span> </p> <p> Open the database for reading only. Any attempt to modify items in the database will fail, regardless of the actual permissions of any underlying files. </p> </li> <li> <p> <span class="bold"><strong>-recnum</strong></span> </p> <p> Support retrieval from the Btree using record numbers. </p> <p> Logical record numbers in Btree databases are mutable in the face of record insertion or deletion. See the <span class="bold"><strong>-renumber</strong></span> argument for further discussion. </p> <p> Maintaining record counts within a Btree introduces a serious point of contention, namely the page locations where the record counts are stored. In addition, the entire tree must be locked during both insertions and deletions, effectively single-threading the tree for those operations. Specifying <span class="bold"><strong>-recnum</strong></span> can result in serious performance degradation for some applications and data sets. </p> <p> It is an error to specify both <span class="bold"><strong>-dup</strong></span> and <span class="bold"><strong>-recnum</strong></span>. </p> </li> <li> <p> <span class="bold"><strong>-renumber</strong></span> </p> <p> Specifying the <span class="bold"><strong>-renumber</strong></span> argument causes the logical record numbers to be mutable, and change as records are added to and deleted from the database. For example, the deletion of record number 4 causes records numbered 5 and greater to be renumbered downward by one. If a cursor was positioned to record number 4 before the deletion, it will refer to the new record number 4, if any such record exists, after the deletion. If a cursor was positioned after record number 4 before the deletion, it will be shifted downward one logical record, continuing to refer to the same record as it did before. </p> <p> Using the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>put</strong></span> or <span class="emphasis"><em>dbc</em></span> <span class="bold"><strong>put</strong></span> interfaces to create new records will cause the creation of multiple records if the record number is more than one greater than the largest record currently in the database. For example, creating record 28 when record 25 was previously the last record in the database, will create records 26 and 27 as well as 28. </p> <p> If a created record is not at the end of the database, all records following the new record will be automatically renumbered upward by one. For example, the creation of a new record numbered 8 causes records numbered 8 and greater to be renumbered upward by one. If a cursor was positioned to record number 8 or greater before the insertion, it will be shifted upward one logical record, continuing to refer to the same record as it did before. </p> <p> For these reasons, concurrent access to a Recno database with the <span class="bold"><strong>-renumber</strong></span> flag specified may be largely meaningless, although it is supported. </p> </li> <li> <p> <span class="bold"><strong>-snapshot</strong></span> </p> <p> This argument specifies that any specified <span class="bold"><strong>-source</strong></span> file be read in its entirety when the database is opened. If this argument is not specified, the <span class="bold"><strong>-source</strong></span> file may be read lazily. </p> </li> <li> <p> <span class="bold"><strong>-source file</strong></span> </p> <p> Set the underlying source file for the Recno access method. The purpose of the <span class="bold"><strong>-source</strong></span> file is to provide fast access and modification to databases that are normally stored as flat text files. </p> <p> If the <span class="bold"><strong>-source</strong></span> argument is give, it specifies an underlying flat text database file that is read to initialize a transient record number index. In the case of variable length records, the records are separated as specified by <span class="bold"><strong>-delim</strong></span>. For example, standard UNIX byte stream files can be interpreted as a sequence of variable length records separated by <newline> characters. </p> <p> In addition, when cached data would normally be written back to the underlying database file (for example, when the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>close</strong></span> or <span class="emphasis"><em>db</em></span> <span class="bold"><strong>sync</strong></span> commands are called), the in-memory copy of the database will be written back to the <span class="bold"><strong>-source</strong></span> file. </p> <p> By default, the backing source file is read lazily, that is, records are not read from the file until they are requested by the application. <span class="bold"><strong>If multiple processes (not threads) are accessing a Recno database concurrently and either inserting or deleting records, the backing source file must be read in its entirety before more than a single process accesses the database, and only that process should specify the backing source argument as part of the <span class="bold"><strong>berkdb open</strong></span> call. See the <span class="bold"><strong>-snapshot</strong></span> argument for more information.</strong></span> </p> <p> <span class="bold"><strong>Reading and writing the backing source file specified by <span class="bold"><strong>-source</strong></span> cannot be transaction protected because it involves filesystem operations that are not part of the Berkeley DB transaction methodology.</strong></span> For this reason, if a temporary database is used to hold the records, it is possible to lose the contents of the <span class="bold"><strong>-source</strong></span> file, for example, if the system crashes at the right instant. If a file is used to hold the database, that is, a filename was specified as the <span class="bold"><strong>file</strong></span> argument to <span class="bold"><strong>berkdb open</strong></span>, normal database recovery on that file can be used to prevent information loss, although it is still possible that the contents of <span class="bold"><strong>-source</strong></span> file will be lost if the system crashes. </p> <p> The <span class="bold"><strong>-source</strong></span> file must already exist (but may be zero-length) when <span class="bold"><strong>berkdb open</strong></span> is called. </p> <p> It is not an error to specify a read-only <span class="bold"><strong>-source</strong></span> file when creating a database, nor is it an error to modify the resulting database. However, any attempt to write the changes to the backing source file using either the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>close</strong></span> or <span class="emphasis"><em>db</em></span> <span class="bold"><strong>sync</strong></span> commands will fail, of course. Specifying the <span class="bold"><strong>-nosync</strong></span> argument to the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>close</strong></span> command will stop it from attempting to write the changes to the backing file; instead, they will be silently discarded. </p> <p> For all of the previous reasons, the <span class="bold"><strong>-source</strong></span> file is generally used to specify databases that are read-only for Berkeley DB applications, and that are either generated on the fly by software tools, or modified using a different mechanism such as a text editor. </p> </li> <li> <p> <span class="bold"><strong>-truncate</strong></span> </p> <p> Physically truncate the underlying file, discarding all previous databases it might have held. Underlying filesystem primitives are used to implement this flag. For this reason, it is only applicable to the physical file and cannot be used to discard databases within a file. </p> <p> The <span class="bold"><strong>-truncate</strong></span> argument cannot be transaction-protected, and it is an error to specify it in a transaction-protected environment. </p> </li> <li> <p> <span class="bold"><strong>-txn txnid</strong></span> </p> <p> If the operation is part of an application-specified transaction, the <span class="bold"><strong>txnid</strong></span> parameter is a transaction handle returned from <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>. If no transaction handle is specified, but the -auto_commit flag is specified, the operation will be implicitly transaction protected. </p> </li> <li> <p> <span class="bold"><strong>--</strong></span> </p> <p> Mark the end of the command arguments. </p> </li> <li> <p> <span class="bold"><strong>file</strong></span> </p> <p> The name of a single physical file on disk that will be used to back the database. </p> <p> An in-memory database never intended to be preserved on disk may be created by not specifying a file name. For example: </p> <pre class="programlisting">berkdb open -create -btree </pre> <p> creates an in-memory database. </p> </li> <li> <p> <span class="bold"><strong>database</strong></span> </p> <p> The <span class="bold"><strong>database</strong></span> argument allows applications to have multiple databases inside of a single physical file. This is useful when the databases are both numerous and reasonably small, in order to avoid creating a large number of underlying files. It is an error to attempt to open a second database file that was not initially created using a <span class="bold"><strong>database</strong></span> name. </p> <p> Applications opening multiple databases in a single file will almost certainly need to create a shared database environment. See <a href="../../programmer_reference/am_opensub.html" class="olink">Opening multiple databases in a single file</a> in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information. </p> <p> If more than one in-memory database is desired, it is necessary to specify an empty string as the database name. For example: </p> <pre class="programlisting">berkdb open -create -btree "" foo berkdb open -create -btree "" bar </pre> <p> will create two databases, neither of which will appear on disk. </p> </li> </ul> </div> <p> The <span class="bold"><strong>berkdb open</strong></span> command returns a database handle on success. </p> <p> In the case of error, a Tcl error is thrown. </p> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="db_join.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="tclapi.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="db_put.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top"><span class="emphasis"><em>db</em></span> join </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> <span class="emphasis"><em>db</em></span> put</td> </tr> </table> </div> </body> </html>