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<h1>Db.open</h1>
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<h3><pre>
import com.sleepycat.db.*;
import java.io.FileNotFoundException;
<p>
public void open(String file,
String database, int type, int flags, int mode)
throws DbException, FileNotFoundException;
</pre></h3>
<h1>Description</h1>
<p>The currently supported Berkeley DB file formats (or <i>access methods</i>)
are Btree, Hash, Queue, and Recno. The Btree format is a representation
of a sorted, balanced tree structure. The Hash format is an extensible,
dynamic hashing scheme. The Queue format supports fast access to
fixed-length records accessed sequentially or by logical record number.
The Recno format supports fixed- or variable-length records, accessed
sequentially or by logical record number, and optionally backed by a
flat text file.
<p>Storage and retrieval for the Berkeley DB access methods are based on key/data
pairs; see <a href="../../db4-devel-4.0.14/api_java/dbt_class.html">Dbt</a> for more information.
<p>The Db.open interface opens the database represented by the
<b>file</b> and <b>database</b> arguments for both reading and
writing. The <b>file</b> argument is used as the name of an underlying
file that will be used to back the database. The <b>database</b>
argument is optional, and allows applications to have multiple databases
in a single file. Although no <b>database</b> argument needs to be
specified, it is an error to attempt to open a second database in a
<b>file</b> that was not initially created using a <b>database</b>
name. Further, the <b>database</b> argument is not supported by the
Queue format.
<p>In-memory databases never intended to be preserved on disk may be
created by setting both the <b>file</b> and <b>database</b> arguments
to null. Note that in-memory databases can only ever be shared by
sharing the single database handle that created them, in circumstances
where doing so is safe.
<p>The <b>type</b> argument is of type int, and must be set to one of Db.DB_BTREE, Db.DB_HASH,
Db.DB_QUEUE, Db.DB_RECNO, or Db.DB_UNKNOWN. If
<b>type</b> is Db.DB_UNKNOWN, the database must already exist
and Db.open will automatically determine its type. The
<a href="../../db4-devel-4.0.14/api_java/db_get_type.html">Db.get_type</a> method may be used to determine the underlying type of
databases opened using Db.DB_UNKNOWN.
<p>The <b>flags</b> and <b>mode</b> arguments specify how files will be opened
and/or created if they do not already exist.
<p>The <b>flags</b> value must be set to 0 or by bitwise inclusively <b>OR</b>'ing together one or
more of the following values:
<p><dl compact>
<p><dt><a name="Db.DB_CREATE">Db.DB_CREATE</a><dd>Create any underlying files, as necessary. If the files do not already
exist and the DB_CREATE flag is not specified, the call will fail.
<p><dt><a name="Db.DB_DIRTY_READ">Db.DB_DIRTY_READ</a><dd>Support dirty reads; that is, transactions, cursors and read operations
in the database may request the return of modified but not yet committed
data.
<p><dt><a name="Db.DB_EXCL">Db.DB_EXCL</a><dd>Return an error if the file already exists. Underlying filesystem
primitives are used to implement this flag. For this reason, it is only
applicable to the file and cannot be used to test whether a database in a
file already exists.
<p>The Db.DB_EXCL flag is only meaningful when specified with the
Db.DB_CREATE flag.
<p><dt><a name="Db.DB_NOMMAP">Db.DB_NOMMAP</a><dd>Do not map this database into process memory (see the description of the
<a href="../../db4-devel-4.0.14/api_java/env_set_mp_mmapsize.html">DbEnv.set_mp_mmapsize</a> method for further information).
<p><dt><a name="Db.DB_RDONLY">Db.DB_RDONLY</a><dd>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><dt><a name="Db.DB_THREAD">Db.DB_THREAD</a><dd>Cause the <a href="../../db4-devel-4.0.14/api_java/db_class.html">Db</a> handle returned by Db.open to be
<i>free-threaded</i>; that is, usable by multiple threads within a
single address space.
<p>Threading is always assumed in the Java API, so no special flags are
required, and Berkeley DB functions will always behave as if the
<a href="../../db4-devel-4.0.14/api_java/env_open.html#DB_THREAD">Db.DB_THREAD</a> flag was specified.
<p><dt><a name="Db.DB_TRUNCATE">Db.DB_TRUNCATE</a><dd>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 applicable only to the
file and cannot be used to discard databases within a file.
<p>The Db.DB_TRUNCATE flag cannot be transaction-protected, and it is
an error to specify it in a transaction-protected environment.
</dl>
<p>On UNIX systems or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by
the access methods are created with mode <b>mode</b> (as described in <b>chmod</b>(2)) and modified by the process' umask value at the time of creation
(see <b>umask</b>(2)). If <b>mode</b> is 0, the access methods will use a default
mode of readable and writable by both owner and group. On Windows
systems, the mode argument is ignored. The group ownership of created
files is based on the system and directory defaults, and is not further
specified by Berkeley DB.
<p>Calling Db.open is a reasonably expensive operation, and
maintaining a set of open databases will normally be preferable to
repeatedly opening and closing the database for each new query.
<p>The Db.open method throws an exception that encapsulates a non-zero error value on
failure.
<h1>Environment Variables</h1>
<p><dl compact>
<p><dt>DB_HOME<dd>If the <b>dbenv</b> argument to <a href="../../db4-devel-4.0.14/api_c/db_create.html">db_create</a> was initialized using
<a href="../../db4-devel-4.0.14/api_java/env_open.html">DbEnv.open</a>, the environment variable <b>DB_HOME</b> may be used
as the path of the database environment home. Specifically, Db.open
is affected by the configuration value DB_DATA_DIR.
</dl>
<p><dl compact>
<p><dt>TMPDIR<dd>If the <b>file</b> and <b>dbenv</b> arguments to Db.open are
null, the environment variable <b>TMPDIR</b> may be used as a
directory in which to create a temporary backing file.
</dl>
<h1>Errors</h1>
<p>The Db.open method may fail and throw an exception encapsulating a non-zero error for the following conditions:
<p><dl compact>
<p><dt><a name="Db.DB_OLD_VERSION">Db.DB_OLD_VERSION</a><dd>The database cannot be opened without being first upgraded.
<p><dt>EEXIST<dd>DB_CREATE and DB_EXCL were specified and the file exists.
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified (for example, unknown
database type, page size, hash function, pad byte, byte order) or a flag
value or parameter that is incompatible with the specified database.
<p>
The <a href="../../db4-devel-4.0.14/api_java/env_open.html#DB_THREAD">Db.DB_THREAD</a> flag was specified and fast mutexes are not
available for this architecture.
<p>The <a href="../../db4-devel-4.0.14/api_java/env_open.html#DB_THREAD">Db.DB_THREAD</a> flag was specified to Db.open, but was not
specified to the <a href="../../db4-devel-4.0.14/api_java/env_open.html">DbEnv.open</a> call for the environment in which the
<a href="../../db4-devel-4.0.14/api_java/db_class.html">Db</a> handle was created.
<p>A backing flat text file was specified with either the <a href="../../db4-devel-4.0.14/api_java/env_open.html#DB_THREAD">Db.DB_THREAD</a>
flag or the provided database environment supports transaction
processing.
<p><dt>ENOENT<dd>A nonexistent <b>re_source</b> file was specified.
</dl>
<p>The Db.open method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the Db.open method may fail and throw
a <a href="../../db4-devel-4.0.14/api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls
will fail in the same way.
<h1>Class</h1>
<a href="../../db4-devel-4.0.14/api_java/db_class.html">Db</a>
<h1>See Also</h1>
<a href="../../db4-devel-4.0.14/api_java/db_associate.html">Db.associate</a>,
<a href="../../db4-devel-4.0.14/api_java/db_close.html">Db.close</a>,
<a href="../../db4-devel-4.0.14/api_java/db_cursor.html">Db.cursor</a>,
<a href="../../db4-devel-4.0.14/api_java/db_del.html">Db.del</a>,
<a href="../../db4-devel-4.0.14/api_java/db_fd.html">Db.fd</a>,
<a href="../../db4-devel-4.0.14/api_java/db_get.html">Db.get</a>,
<a href="../../db4-devel-4.0.14/api_java/db_get.html">Db.pget</a>,
<a href="../../db4-devel-4.0.14/api_java/db_get_byteswapped.html">Db.get_byteswapped</a>,
<a href="../../db4-devel-4.0.14/api_java/db_get_type.html">Db.get_type</a>,
<a href="../../db4-devel-4.0.14/api_java/db_join.html">Db.join</a>,
<a href="../../db4-devel-4.0.14/api_java/db_key_range.html">Db.key_range</a>,
<a href="../../db4-devel-4.0.14/api_java/db_open.html">Db.open</a>,
<a href="../../db4-devel-4.0.14/api_java/db_put.html">Db.put</a>,
<a href="../../db4-devel-4.0.14/api_java/db_remove.html">Db.remove</a>,
<a href="../../db4-devel-4.0.14/api_java/db_rename.html">Db.rename</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_append_recno.html">Db.set_append_recno</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_bt_minkey.html">Db.set_bt_minkey</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_cachesize.html">Db.set_cachesize</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_errcall.html">Db.set_errcall</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_errpfx.html">Db.set_errpfx</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_feedback.html">Db.set_feedback</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_flags.html">Db.set_flags</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_h_ffactor.html">Db.set_h_ffactor</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_h_nelem.html">Db.set_h_nelem</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_lorder.html">Db.set_lorder</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_pagesize.html">Db.set_pagesize</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_q_extentsize.html">Db.set_q_extentsize</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_re_delim.html">Db.set_re_delim</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_re_len.html">Db.set_re_len</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_re_pad.html">Db.set_re_pad</a>,
<a href="../../db4-devel-4.0.14/api_java/db_set_re_source.html">Db.set_re_source</a>,
<a href="../../db4-devel-4.0.14/api_java/db_stat.html">Db.stat</a>,
<a href="../../db4-devel-4.0.14/api_java/db_sync.html">Db.sync</a>,
<a href="../../db4-devel-4.0.14/api_java/db_truncate.html">Db.truncate</a>,
<a href="../../db4-devel-4.0.14/api_java/db_upgrade.html">Db.upgrade</a>,
and
<a href="../../db4-devel-4.0.14/api_java/db_verify.html">Db.verify</a>.
</tt>
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