<!--$Id: log_get.so,v 10.22 2000/03/17 01:53:59 bostic Exp $--> <!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <html> <head> <title>Berkeley DB: DbEnv.log_get</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table><tr valign=top> <td> <h1>DbEnv.log_get</h1> </td> <td width="1%"> <a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> import com.sleepycat.db.*; <p> public void log_get(DbLsn lsn, Dbt data, int flags) throws DbException; </pre></h3> <h1>Description</h1> <p>The DbEnv.log_get method implements a cursor inside of the log, retrieving records from the log according to the <b>lsn</b> and <b>flags</b> arguments. <p>The data field of the <b>data</b> structure is set to the record retrieved and the size field indicates the number of bytes in the record. See <a href="../api_java/dbt_class.html">Dbt</a> for a description of other fields in the <b>data</b> structure. When multiple threads are using the returned log handle concurrently, one of the <a href="../api_java/dbt_class.html#DB_DBT_MALLOC">Db.DB_DBT_MALLOC</a>, <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 for any <a href="../api_java/dbt_class.html">Dbt</a> used for data retrieval. <p>The <b>flags</b> argument must be set to exactly one of the following values: <p><dl compact> <p><dt><a name="Db.DB_CHECKPOINT">Db.DB_CHECKPOINT</a><dd>The last record written with the DB_CHECKPOINT flag specified to the <a href="../api_java/log_put.html">DbEnv.log_put</a> method is returned in the <b>data</b> argument. The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record returned. If no record has been previously written with the DB_CHECKPOINT flag specified, the first record in the log is returned. <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>. <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 is returned in the <b>data</b> argument. The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record returned. <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>. <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. The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record returned. <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>. <p><dt><a name="Db.DB_NEXT">Db.DB_NEXT</a><dd>The current log position is advanced to the next record in the log and that record is returned in the <b>data</b> argument. The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record returned. <p>If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, DbEnv.log_get will return the first record in the log. If the last log record has already been returned or the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>. <p>If the log was opened with the DB_THREAD flag set, calls to DbEnv.log_get with the DB_NEXT flag set will return EINVAL. <p><dt><a name="Db.DB_PREV">Db.DB_PREV</a><dd>The current log position is moved to the previous record in the log and that record is returned in the <b>data</b> argument. The <b>lsn</b> argument is overwritten with the <a href="../api_java/lsn_class.html">DbLsn</a> of the record returned. <p>If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, DbEnv.log_get will return the last record in the log. If the first log record has already been returned or the log is empty, the DbEnv.log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>. <p>If the log was opened with the DB_THREAD flag set, calls to DbEnv.log_get with the DB_PREV flag set will return EINVAL. <p><dt><a name="Db.DB_CURRENT">Db.DB_CURRENT</a><dd>Return the log record currently referenced by the log. <p>If the log pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET, DB_NEXT, or DB_PREV, or if the log was opened with the DB_THREAD flag set, DbEnv.log_get will return EINVAL. <p><dt><a name="Db.DB_SET">Db.DB_SET</a><dd>Retrieve the record specified by the <b>lsn</b> argument. If the specified <a href="../api_java/lsn_class.html">DbLsn</a> is invalid (e.g., does not appear in the log) DbEnv.log_get will return EINVAL. </dl> <p>Otherwise, the DbEnv.log_get method throws an exception that encapsulates a non-zero error value on failure. <h1>Errors</h1> <p>The DbEnv.log_get method may fail and throw an exception encapsulating a non-zero error for the following conditions: <p><dl compact> <p><dt>EINVAL<dd>An invalid flag value or parameter was specified. <p>The DB_FIRST flag was specified and no log files were found. </dl> <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. If a catastrophic error has occurred, the DbEnv.log_get method may fail and throw a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls will fail in the same way. <h3>Class</h3> <a href="../api_java/dbenv_class.html">DbEnv</a> <h1>See Also</h1> <a href="../api_java/env_set_lg_bsize.html">DbEnv.set_lg_bsize</a>, <a href="../api_java/env_set_lg_max.html">DbEnv.set_lg_max</a>, <a href="../api_java/log_archive.html">DbEnv.log_archive</a>, <a href="../api_java/log_compare.html">DbEnv.log_compare</a>, <a href="../api_java/log_file.html">DbEnv.log_file</a>, <a href="../api_java/log_flush.html">DbEnv.log_flush</a>, <a href="../api_java/log_get.html">DbEnv.log_get</a>, <a href="../api_java/log_put.html">DbEnv.log_put</a>, <a href="../api_java/log_register.html">DbEnv.log_register</a>, <a href="../api_java/log_stat.html">DbEnv.log_stat</a> and <a href="../api_java/log_unregister.html">DbEnv.log_unregister</a>. </tt> <table><tr><td><br></td><td width="1%"> <a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> </body> </html>