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478 lines
19 KiB
HTML
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DB->compact()</title>
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<link rel="up" href="db.html" title="Chapter 2. The DB Handle" />
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<link rel="prev" href="dbclose.html" title="DB->close()" />
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<div xmlns="" class="navheader">
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<p>Library Version 11.2.5.3</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DB->compact()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbclose.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The DB Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="db_copy.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="dbcompact"></a>DB->compact()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB->compact(DB *db, DB_TXN *txnid,
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DBT *start, DBT *stop, DB_COMPACT *c_data, u_int32_t flags, DBT *end); </pre>
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<p>
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The <code class="methodname">DB->compact()</code> method compacts Btree,
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Hash, and Recno access method databases, and optionally returns
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unused Btree, Hash or Recno database pages to the underlying
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filesystem.
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</p>
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<p>
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The <code class="methodname">DB->compact()</code> <span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="idp57374568"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57273192"></a>txnid</h4>
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</div>
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</div>
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</div>
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<p>
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If the operation is part of an application-specified transaction, the
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<span class="bold"><strong>txnid</strong></span> parameter is a transaction
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handle returned from <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>;
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if the operation is part of a Berkeley DB Concurrent Data Store group, the
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<span class="bold"><strong>txnid</strong></span> parameter is a handle returned
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from <a class="xref" href="envcdsgroup_begin.html" title="DB_ENV->cdsgroup_begin()">DB_ENV->cdsgroup_begin()</a>;
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otherwise NULL.
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</p>
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<p>
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If a transaction handle is supplied to this method, then the operation is
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performed using that transaction. In this event, large sections of the
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tree may be locked during the course of the transaction.
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</p>
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<p>
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If no transaction handle is specified, but the operation occurs
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in a transactional database, the operation will be implicitly
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transaction protected using multiple transactions. These transactions
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will be periodically committed to avoid locking large sections of the
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tree. Any deadlocks encountered cause the compaction operation to
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be retried from the point of the last transaction commit.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57371008"></a>start</h4>
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</div>
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</div>
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</div>
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<p>
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If non-NULL, the <span class="bold"><strong>start</strong></span>
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parameter is the starting point for compaction. For a
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Btree or Recno database, compaction will start at the
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smallest key greater than or equal to the specified key.
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For a Hash database, the compaction will start in the
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bucket specified by the integer stored in the key. If
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NULL, compaction will start at the beginning of the
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database.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57272480"></a>stop</h4>
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</div>
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</div>
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</div>
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<p>
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If non-NULL, the <span class="bold"><strong>stop</strong></span>
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parameter is the stopping point for compaction. For a
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Btree or Recno database, compaction will stop at the page
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with the smallest key greater than the specified key.
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For a Hash database, compaction will stop in the bucket
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specified by the integer stored in the key. If NULL,
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compaction will stop at the end of the database.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57351192"></a>c_data</h4>
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</div>
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</div>
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</div>
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<p>
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If non-NULL, the <span class="bold"><strong>c_data</strong></span> parameter
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contains additional compaction configuration parameters, and returns
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compaction operation statistics, in a structure of type
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<code class="literal">DB_COMPACT</code>.
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</p>
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<p>
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The following input configuration fields are available from the
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<code class="literal">DB_COMPACT</code> structure:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">int compact_fillpercent;</code>
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</p>
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<p>
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If non-zero, this provides the goal for filling
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pages, specified as a percentage between 1 and 100.
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Any page in the database not at or above this
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percentage full will be considered for compaction.
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The default behavior is to consider every page for
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compaction, regardless of its page fill percentage.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">int compact_pages;</code>
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</p>
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<p>
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If non-zero, the call will return after the
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specified number of pages have been freed, or no
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more pages can be freed.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">db_timeout_t compact_timeout;</code>
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</p>
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<p>
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If non-zero, and no
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<span class="bold"><strong>txnid</strong></span> parameter was
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specified, this parameter identifies the lock
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timeout used for implicit transactions, in
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microseconds.
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</p>
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</li>
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</ul>
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</div>
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<p>
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The following output statistics fields are available from the
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<code class="literal">DB_COMPACT</code> structure:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">u_int32_t compact_deadlock;</code>
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</p>
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<p>
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An output statistics parameter: if no
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<span class="bold"><strong>txnid</strong></span> parameter was
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specified, the number of deadlocks which occurred.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">u_int32_t compact_pages_examine;</code>
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</p>
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<p>
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An output statistics parameter: the number of
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database pages reviewed during the compaction
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phase.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">u_int32_t compact_empty_buckets;</code>
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</p>
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<p>
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An output statistics parameter: the number of empty
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hash buckets that were found the compaction phase.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">u_int32_t compact_pages_free;</code>
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</p>
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<p>
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An output statistics parameter: the number of
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database pages freed during the compaction phase.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">u_int32_t compact_levels;</code>
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</p>
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<p>
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An output statistics parameter: the number of levels
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removed from the Btree or Recno database during the
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compaction phase.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">u_int32_t compact_pages_truncated;</code>
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</p>
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<p>
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An output statistics parameter: the number of
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database pages returned to the filesystem.
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</p>
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</li>
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</ul>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57378048"></a>flags</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
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or one of the following values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="compact_DB_FREELIST_ONLY"></a>
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<code class="literal">DB_FREELIST_ONLY</code>
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</p>
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<p>
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Do no page compaction, only returning pages to the
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filesystem that are already free and at the end of
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the file.
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</p>
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</li>
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<li>
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<p><a id="compact_DB_FREE_SPACE"></a>
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<code class="literal">DB_FREE_SPACE</code>
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</p>
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<p>
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Return pages to the filesystem when possible. If
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this flag is not specified, pages emptied as a
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result of compaction will be placed on the free
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list for re-use, but never returned to the
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filesystem.
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</p>
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<p>
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Note that only pages at the end of a file can be
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returned to the filesystem. Because of the
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one-pass nature of the compaction algorithm, any
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unemptied page near the end of the file inhibits
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returning pages to the file system. A repeated
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call to the <code class="methodname">DB->compact()</code>
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method with a low
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<span class="bold"><strong>compact_fillpercent</strong></span>
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may be used to return pages in this case.
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</p>
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</li>
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</ul>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp57403632"></a>end</h4>
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</div>
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</div>
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</div>
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<p>
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If non-NULL, the <span class="bold"><strong>end</strong></span>
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parameter will be filled with the database key marking
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the end of the compaction operation in a Btree or Recno
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database. This is generally the first key of the page
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where the operation stopped. For a Hash database, this
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will hold the integer value representing which bucket the
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compaction stopped in.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="idp57402104"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DB->compact()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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||
<div class="titlepage">
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||
<div>
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<div>
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<h4 class="title"><a id="idp57393680"></a>DB_LOCK_DEADLOCK</h4>
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</div>
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</div>
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</div>
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<p>
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A transactional database environment operation was selected to resolve
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a deadlock.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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||
<div class="titlepage">
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||
<div>
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<div>
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<h4 class="title"><a id="idp57390240"></a>DB_LOCK_NOTGRANTED</h4>
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</div>
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</div>
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</div>
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<p>
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||
A Berkeley DB Concurrent Data Store database environment configured
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||
for lock timeouts was unable to grant a lock in the allowed time.
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||
</p>
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<p>
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||
You attempted to open a database handle that is configured
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||
for no waiting exclusive locking, but the exclusive lock could not be
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immediately obtained. See
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<a class="xref" href="dbset_lk_exclusive.html" title="DB->set_lk_exclusive()">DB->set_lk_exclusive()</a>
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for more information.
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||
</p>
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||
</div>
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||
<div class="sect3" lang="en" xml:lang="en">
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||
<div class="titlepage">
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||
<div>
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||
<div>
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<h4 class="title"><a id="idp57399816"></a> DB_REP_HANDLE_DEAD</h4>
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</div>
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</div>
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</div>
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<p>
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When a client synchronizes with the master, it is possible for committed
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||
transactions to be rolled back. This invalidates all the database and cursor
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handles opened in the replication environment. Once this occurs, an attempt to use
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||
such a handle will
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return <code class="literal">DB_REP_HANDLE_DEAD</code>.
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||
The application will need to discard the handle and open a new one in order to
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||
continue processing.
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||
</p>
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||
</div>
|
||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
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||
<div>
|
||
<h4 class="title"><a id="idp57410216"></a>DB_REP_LOCKOUT</h4>
|
||
</div>
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||
</div>
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||
</div>
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<p>
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The operation was blocked by client/master synchronization.
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||
</p>
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||
</div>
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||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h4 class="title"><a id="idp57398776"></a>EACCES</h4>
|
||
</div>
|
||
</div>
|
||
</div>
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||
<p>
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||
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="idp57385880"></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="idp57408152"></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="idp57402512"></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>
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||
<td width="40%" align="right" valign="top"> db_copy</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
|