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6.5 KiB
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<!--$Id: log_get.so,v 10.22 2000/03/17 01:53:59 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<html>
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<head>
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<title>Berkeley DB: log_get</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
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<body bgcolor=white>
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<a name="2"><!--meow--></a>
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<table><tr valign=top>
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<td>
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<h1>log_get</h1>
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</td>
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<td width="1%">
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<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<hr size=1 noshade>
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<tt>
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<h3><pre>
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#include <db.h>
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<p>
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int
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log_get(DB_ENV *env, DB_LSN *lsn, DBT *data, u_int32_t flags);
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</pre></h3>
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<h1>Description</h1>
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<p>The log_get function 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 record.
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See <a href="../api_c/dbt.html">DBT</a> for a description of other fields in the <b>data</b>
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structure. When multiple threads are using the returned log handle
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concurrently, one of the <a href="../api_c/dbt.html#DB_DBT_MALLOC">DB_DBT_MALLOC</a>, <a href="../api_c/dbt.html#DB_DBT_REALLOC">DB_DBT_REALLOC</a> or
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<a href="../api_c/dbt.html#DB_DBT_USERMEM">DB_DBT_USERMEM</a> flags must be specified for any <a href="../api_c/dbt.html">DBT</a> used
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for data retrieval.
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<p>The <b>flags</b> argument must be set to exactly one of the following values:
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<p><dl compact>
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<p><dt><a name="DB_CHECKPOINT">DB_CHECKPOINT</a><dd>The last record written with the DB_CHECKPOINT flag specified to the
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<a href="../api_c/log_put.html">log_put</a> function is returned in the <b>data</b> argument. The
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<b>lsn</b> argument is overwritten with the <a href="../api_c/db_lsn.html">DB_LSN</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 log_get function will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
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<p><dt><a name="DB_FIRST">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_c/db_lsn.html">DB_LSN</a> of the
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record returned.
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<p>If the log is empty, the log_get function will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
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<p><dt><a name="DB_LAST">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_c/db_lsn.html">DB_LSN</a> of the
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record returned.
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<p>If the log is empty, the log_get function will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
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<p><dt><a name="DB_NEXT">DB_NEXT</a><dd>The current log position is advanced to the next record in the log and that
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record is returned in the <b>data</b> argument.
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The <b>lsn</b> argument is overwritten with the <a href="../api_c/db_lsn.html">DB_LSN</a> of the
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record returned.
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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, log_get will return the first record in the log.
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If the last log record has already been returned or the log is empty, the
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log_get function will return <a href="../ref/program/errorret.html#DB_NOTFOUND">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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log_get with the DB_NEXT flag set will return EINVAL.
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<p><dt><a name="DB_PREV">DB_PREV</a><dd>The current log position is moved to the previous record in the log and that
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record is returned in the <b>data</b> argument.
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The <b>lsn</b> argument is overwritten with the <a href="../api_c/db_lsn.html">DB_LSN</a> of the
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record returned.
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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,
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log_get will return the last record in the log.
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If the first log record has already been returned or the log is empty, the
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log_get function will return <a href="../ref/program/errorret.html#DB_NOTFOUND">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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log_get with the DB_PREV flag set will return EINVAL.
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<p><dt><a name="DB_CURRENT">DB_CURRENT</a><dd>Return the log record currently referenced by the log.
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<p>If the log pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET,
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DB_NEXT, or DB_PREV, or if the log was opened with the DB_THREAD flag set,
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log_get will return EINVAL.
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<p><dt><a name="DB_SET">DB_SET</a><dd>Retrieve the record specified by the <b>lsn</b> argument. If the
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specified <a href="../api_c/db_lsn.html">DB_LSN</a> is invalid (e.g., does not appear in the log)
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log_get will return EINVAL.
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</dl>
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<p>Otherwise, the log_get function returns a non-zero error value on failure and 0 on success.
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<h1>Errors</h1>
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<p>The log_get function may fail and return a non-zero error for the following conditions:
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<p><dl compact>
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>The DB_FIRST flag was specified and no log files were found.
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</dl>
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<p>The log_get function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
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If a catastrophic error has occurred, the log_get function may fail and return
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<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
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in the same way.
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<h1>See Also</h1>
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<a href="../api_c/env_set_lg_bsize.html">DBENV->set_lg_bsize</a>,
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<a href="../api_c/env_set_lg_max.html">DBENV->set_lg_max</a>,
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<a href="../api_c/log_archive.html">log_archive</a>,
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<a href="../api_c/log_compare.html">log_compare</a>,
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<a href="../api_c/log_file.html">log_file</a>,
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<a href="../api_c/log_flush.html">log_flush</a>,
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<a href="../api_c/log_get.html">log_get</a>,
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<a href="../api_c/log_put.html">log_put</a>,
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<a href="../api_c/log_register.html">log_register</a>,
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<a href="../api_c/log_stat.html">log_stat</a>
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and
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<a href="../api_c/log_unregister.html">log_unregister</a>.
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</tt>
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<table><tr><td><br></td><td width="1%">
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<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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