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<!--$Id: log_get.so,v 10.27 2001/05/05 01:49:15 bostic Exp $-->
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<title>Berkeley DB: DbEnv.log_get</title>
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<h1>DbEnv.log_get</h1>
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<a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
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import com.sleepycat.db.*;
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public void log_get(DbLsn lsn, Dbt data, int flags)
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<p>The DbEnv.log_get method implements a cursor inside of the log,
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retrieving records from the log according to the <b>lsn</b> and
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<b>flags</b> arguments.
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<p>The data field of the <b>data</b> structure is set to the record
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retrieved, and the size field indicates the number of bytes in the
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record. See <a href="../api_java/dbt_class.html">Dbt</a> for a description of other fields in the
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<b>data</b> structure. When multiple threads are using the
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<a href="../api_java/dbenv_class.html">DbEnv</a> handle concurrently, one of the <a href="../api_java/dbt_class.html#DB_DBT_MALLOC">Db.DB_DBT_MALLOC</a>,
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<a href="../api_java/dbt_class.html#DB_DBT_REALLOC">Db.DB_DBT_REALLOC</a>, or <a href="../api_java/dbt_class.html#DB_DBT_USERMEM">Db.DB_DBT_USERMEM</a> flags must be specified
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for any <a href="../api_java/dbt_class.html">Dbt</a> used for data retrieval.
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<p>The <b>flags</b> value must be set to one of the following values:
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<p><dt><a name="Db.DB_CHECKPOINT">Db.DB_CHECKPOINT</a><dd>The last record written with the DB_CHECKPOINT flag specified to the
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<a href="../api_java/log_put.html">DbEnv.log_put</a> method is returned in the <b>data</b> argument. The
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<b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record
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returned. If no record has been previously written with the DB_CHECKPOINT
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flag specified, the first record in the log is returned.
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<p>If the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_FIRST">Db.DB_FIRST</a><dd>The first record from any of the log files found in the log directory
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is returned in the <b>data</b> argument.
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The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the
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<p>If the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_LAST">Db.DB_LAST</a><dd>The last record in the log is returned in the <b>data</b> argument.
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The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the
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<p>If the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_NEXT">Db.DB_NEXT</a>, <a name="Db.DB_PREV">Db.DB_PREV</a><dd>The current log position is advanced to the next (previous) record in
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the log, and that record is returned in the <b>data</b> argument. The
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<b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record
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<p>If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET,
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DB_NEXT, or DB_PREV, DbEnv.log_get will return the first (last) record
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in the log. If the last (first) log record has already been returned
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or the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p>If the log was opened with the DB_THREAD flag set, calls to
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DbEnv.log_get with the DB_NEXT (DB_PREV) flag set will return
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<p><dt><a name="Db.DB_CURRENT">Db.DB_CURRENT</a><dd>Return the log record to which the log currently refers.
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<p>If the log pointer has not been initialized via DB_FIRST, DB_LAST,
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DB_SET, DB_NEXT, or DB_PREV, or if the log was opened with the DB_THREAD
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flag set, DbEnv.log_get will return EINVAL.
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<p><dt><a name="Db.DB_SET">Db.DB_SET</a><dd>Retrieve the record specified by the <b>lsn</b> argument. If the
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specified <a href="../api_java/lsn_class.html">DbLsn</a> is invalid (for example, it does not appear in
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the log) DbEnv.log_get will return EINVAL.
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<p>Otherwise, the DbEnv.log_get method throws an exception that encapsulates a non-zero error value on
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<p>The DbEnv.log_get method may fail and throw an exception encapsulating a non-zero error for the following conditions:
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>The DB_NEXT or DB_PREV flags were set and the log was opened with the
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<p>The DB_CURRENT flag was set and the log pointer had not yet been
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<p>The DB_SET flag was set and the specified log sequence number does not
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<p>The DbEnv.log_get method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods.
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If a catastrophic error has occurred, the DbEnv.log_get method may fail and throw
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a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls
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will fail in the same way.
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<a href="../api_java/dbenv_class.html">DbEnv</a>
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<a href="../api_java/env_set_lg_bsize.html">DbEnv.set_lg_bsize</a>,
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<a href="../api_java/env_set_lg_dir.html">DbEnv.set_lg_dir</a>,
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<a href="../api_java/env_set_lg_max.html">DbEnv.set_lg_max</a>,
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<a href="../api_java/env_set_lg_regionmax.html">DbEnv.set_lg_regionmax</a>,
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<a href="../api_java/log_archive.html">DbEnv.log_archive</a>,
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<a href="../api_java/log_compare.html">DbEnv.log_compare</a>,
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<a href="../api_java/log_file.html">DbEnv.log_file</a>,
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<a href="../api_java/log_flush.html">DbEnv.log_flush</a>,
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<a href="../api_java/log_get.html">DbEnv.log_get</a>,
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<a href="../api_java/log_put.html">DbEnv.log_put</a>,
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<a href="../api_java/log_register.html">DbEnv.log_register</a>,
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<a href="../api_java/log_stat.html">DbEnv.log_stat</a>,
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<a href="../api_java/log_unregister.html">DbEnv.log_unregister</a>.
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