<?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>DB->compact()</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 C API Reference" /> <link rel="up" href="db.html" title="Chapter 2. The DB Handle" /> <link rel="prev" href="dbclose.html" title="DB->close()" /> <link rel="next" href="db_copy.html" title="db_copy" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 11.2.5.3</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DB->compact()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbclose.html">Prev</a> </td> <th width="60%" align="center">Chapter 2. The DB Handle </th> <td width="20%" align="right"> <a accesskey="n" href="db_copy.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="dbcompact"></a>DB->compact()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB->compact(DB *db, DB_TXN *txnid, DBT *start, DBT *stop, DB_COMPACT *c_data, u_int32_t flags, DBT *end); </pre> <p> The <code class="methodname">DB->compact()</code> method compacts Btree, Hash, and Recno access method databases, and optionally returns unused Btree, Hash or Recno database pages to the underlying filesystem. </p> <p> The <code class="methodname">DB->compact()</code> <span> <span> method returns a non-zero error value on failure and 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp49300048"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49291016"></a>txnid</h4> </div> </div> </div> <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 <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the <span class="bold"><strong>txnid</strong></span> parameter is a handle returned from <a class="xref" href="envcdsgroup_begin.html" title="DB_ENV->cdsgroup_begin()">DB_ENV->cdsgroup_begin()</a>; otherwise NULL. </p> <p> If a transaction handle is supplied to this method, then the operation is performed using that transaction. In this event, large sections of the tree may be locked during the course of the transaction. </p> <p> If no transaction handle is specified, but the operation occurs in a transactional database, the operation will be implicitly transaction protected using multiple transactions. These transactions will be periodically committed to avoid locking large sections of the tree. Any deadlocks encountered cause the compaction operation to be retried from the point of the last transaction commit. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49364280"></a>start</h4> </div> </div> </div> <p> If non-NULL, the <span class="bold"><strong>start</strong></span> parameter is the starting point for compaction. For a Btree or Recno database, compaction will start at the smallest key greater than or equal to the specified key. For a Hash database, the compaction will start in the bucket specified by the integer stored in the key. If NULL, compaction will start at the beginning of the database. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49235384"></a>stop</h4> </div> </div> </div> <p> If non-NULL, the <span class="bold"><strong>stop</strong></span> parameter is the stopping point for compaction. For a Btree or Recno database, compaction will stop at the page with the smallest key greater than the specified key. For a Hash database, compaction will stop in the bucket specified by the integer stored in the key. If NULL, compaction will stop at the end of the database. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49216144"></a>c_data</h4> </div> </div> </div> <p> If non-NULL, the <span class="bold"><strong>c_data</strong></span> parameter contains additional compaction configuration parameters, and returns compaction operation statistics, in a structure of type <code class="literal">DB_COMPACT</code>. </p> <p> The following input configuration fields are available from the <code class="literal">DB_COMPACT</code> structure: </p> <div class="itemizedlist"> <ul type="disc"> <li> <p> <code class="literal">int compact_fillpercent;</code> </p> <p> If non-zero, this provides the goal for filling pages, specified as a percentage between 1 and 100. Any page in the database not at or above this percentage full will be considered for compaction. The default behavior is to consider every page for compaction, regardless of its page fill percentage. </p> </li> <li> <p> <code class="literal">int compact_pages;</code> </p> <p> If non-zero, the call will return after the specified number of pages have been freed, or no more pages can be freed. </p> </li> <li> <p> <code class="literal">db_timeout_t compact_timeout;</code> </p> <p> If non-zero, and no <span class="bold"><strong>txnid</strong></span> parameter was specified, this parameter identifies the lock timeout used for implicit transactions, in microseconds. </p> </li> </ul> </div> <p> The following output statistics fields are available from the <code class="literal">DB_COMPACT</code> structure: </p> <div class="itemizedlist"> <ul type="disc"> <li> <p> <code class="literal">u_int32_t compact_deadlock;</code> </p> <p> An output statistics parameter: if no <span class="bold"><strong>txnid</strong></span> parameter was specified, the number of deadlocks which occurred. </p> </li> <li> <p> <code class="literal">u_int32_t compact_pages_examine;</code> </p> <p> An output statistics parameter: the number of database pages reviewed during the compaction phase. </p> </li> <li> <p> <code class="literal">u_int32_t compact_empty_buckets;</code> </p> <p> An output statistics parameter: the number of empty hash buckets that were found the compaction phase. </p> </li> <li> <p> <code class="literal">u_int32_t compact_pages_free;</code> </p> <p> An output statistics parameter: the number of database pages freed during the compaction phase. </p> </li> <li> <p> <code class="literal">u_int32_t compact_levels;</code> </p> <p> An output statistics parameter: the number of levels removed from the Btree or Recno database during the compaction phase. </p> </li> <li> <p> <code class="literal">u_int32_t compact_pages_truncated;</code> </p> <p> An output statistics parameter: the number of database pages returned to the filesystem. </p> </li> </ul> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49398720"></a>flags</h4> </div> </div> </div> <p> The <span class="bold"><strong>flags</strong></span> parameter must be set to 0 or one of the following values: </p> <div class="itemizedlist"> <ul type="disc"> <li> <p><a id="compact_DB_FREELIST_ONLY"></a> <code class="literal">DB_FREELIST_ONLY</code> </p> <p> Do no page compaction, only returning pages to the filesystem that are already free and at the end of the file. </p> </li> <li> <p><a id="compact_DB_FREE_SPACE"></a> <code class="literal">DB_FREE_SPACE</code> </p> <p> Return pages to the filesystem when possible. If this flag is not specified, pages emptied as a result of compaction will be placed on the free list for re-use, but never returned to the filesystem. </p> <p> Note that only pages at the end of a file can be returned to the filesystem. Because of the one-pass nature of the compaction algorithm, any unemptied page near the end of the file inhibits returning pages to the file system. A repeated call to the <code class="methodname">DB->compact()</code> method with a low <span class="bold"><strong>compact_fillpercent</strong></span> may be used to return pages in this case. </p> </li> </ul> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49416288"></a>end</h4> </div> </div> </div> <p> If non-NULL, the <span class="bold"><strong>end</strong></span> parameter will be filled with the database key marking the end of the compaction operation in a Btree or Recno database. This is generally the first key of the page where the operation stopped. For a Hash database, this will hold the integer value representing which bucket the compaction stopped in. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp49392784"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DB->compact()</code> <span> <span> method may fail and return one of the following non-zero errors: </span> </span> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49382944"></a>DB_LOCK_DEADLOCK</h4> </div> </div> </div> <p> A transactional database environment operation was selected to resolve a deadlock. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49415232"></a>DB_LOCK_NOTGRANTED</h4> </div> </div> </div> <p> A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time. </p> <p> You attempted to open a database handle that is configured for no waiting exclusive locking, but the exclusive lock could not be immediately obtained. See <a class="xref" href="dbset_lk_exclusive.html" title="DB->set_lk_exclusive()">DB->set_lk_exclusive()</a> for more information. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49414624"></a> DB_REP_HANDLE_DEAD</h4> </div> </div> </div> <p> When a client synchronizes with the master, it is possible for committed transactions to be rolled back. This invalidates all the database and cursor handles opened in the replication environment. Once this occurs, an attempt to use such a handle will return <code class="literal">DB_REP_HANDLE_DEAD</code>. The application will need to discard the handle and open a new one in order to continue processing. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49427920"></a>DB_REP_LOCKOUT</h4> </div> </div> </div> <p> The operation was blocked by client/master synchronization. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49425952"></a>EACCES</h4> </div> </div> </div> <p> An attempt was made to modify a read-only database. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp49423920"></a>EINVAL</h4> </div> </div> </div> <p> An invalid flag value or parameter was specified. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp49393960"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp49413392"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="dbclose.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="db.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="db_copy.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DB->close() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> db_copy</td> </tr> </table> </div> </body> </html>