140 lines
5.3 KiB
HTML
140 lines
5.3 KiB
HTML
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<title>Write-Ahead Log Commit Hook</title>
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<!-- keywords: sqlite3_wal_hook -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Write-Ahead Log Commit Hook</h2>
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</div>
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<blockquote><pre>
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void *sqlite3_wal_hook(
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sqlite3*,
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int(*)(void *,sqlite3*,const char*,int),
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void*
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);
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</pre></blockquote>
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<p>
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The <a href="../c3ref/wal_hook.html">sqlite3_wal_hook()</a> function is used to register a callback that
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is invoked each time data is committed to a database in wal mode.</p>
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<p>The callback is invoked by SQLite after the commit has taken place and
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the associated write-lock on the database released, so the implementation
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may read, write or <a href="../wal.html#ckpt">checkpoint</a> the database as required.</p>
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<p>The first parameter passed to the callback function when it is invoked
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is a copy of the third parameter passed to sqlite3_wal_hook() when
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registering the callback. The second is a copy of the database handle.
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The third parameter is the name of the database that was written to -
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either "main" or the name of an <a href="../lang_attach.html">ATTACH</a>-ed database. The fourth parameter
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is the number of pages currently in the write-ahead log file,
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including those that were just committed.</p>
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<p>The callback function should normally return <a href="../rescode.html#ok">SQLITE_OK</a>. If an error
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code is returned, that error will propagate back up through the
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SQLite code base to cause the statement that provoked the callback
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to report an error, though the commit will have still occurred. If the
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callback returns <a href="../rescode.html#row">SQLITE_ROW</a> or <a href="../rescode.html#done">SQLITE_DONE</a>, or if it returns a value
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that does not correspond to any valid SQLite error code, the results
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are undefined.</p>
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<p>A single database handle may have at most a single write-ahead log callback
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registered at one time. Calling <a href="../c3ref/wal_hook.html">sqlite3_wal_hook()</a> replaces any
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previously registered write-ahead log callback. Note that the
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<a href="../c3ref/wal_autocheckpoint.html">sqlite3_wal_autocheckpoint()</a> interface and the
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<a href="../pragma.html#pragma_wal_autocheckpoint">wal_autocheckpoint pragma</a> both invoke <a href="../c3ref/wal_hook.html">sqlite3_wal_hook()</a> and will
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overwrite any prior <a href="../c3ref/wal_hook.html">sqlite3_wal_hook()</a> settings.
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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