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+<!-- keywords: sqlite3_wal_checkpoint_v2 -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Checkpoint a database</h2>
+</div>
+<blockquote><pre>
+int sqlite3_wal_checkpoint_v2(
+  sqlite3 *db,                    /* Database handle */
+  const char *zDb,                /* Name of attached database (or NULL) */
+  int eMode,                      /* SQLITE_CHECKPOINT_* value */
+  int *pnLog,                     /* OUT: Size of WAL log in frames */
+  int *pnCkpt                     /* OUT: Total number of frames checkpointed */
+);
+</pre></blockquote>
+<p>
+The sqlite3_wal_checkpoint_v2(D,X,M,L,C) interface runs a checkpoint
+operation on database X of <a href="../c3ref/sqlite3.html">database connection</a> D in mode M.  Status
+information is written back into integers pointed to by L and C.
+The M parameter must be a valid <a href="../c3ref/c_checkpoint_full.html">checkpoint mode</a>:</p>
+
+<p><dl>
+<dt>SQLITE_CHECKPOINT_PASSIVE<dd>
+Checkpoint as many frames as possible without waiting for any database
+readers or writers to finish, then sync the database file if all frames
+in the log were checkpointed. The <a href="../c3ref/busy_handler.html">busy-handler callback</a>
+is never invoked in the SQLITE_CHECKPOINT_PASSIVE mode.
+On the other hand, passive mode might leave the checkpoint unfinished
+if there are concurrent readers or writers.</p>
+
+<p><dt>SQLITE_CHECKPOINT_FULL<dd>
+This mode blocks (it invokes the
+<a href="../c3ref/busy_handler.html">busy-handler callback</a>) until there is no
+database writer and all readers are reading from the most recent database
+snapshot. It then checkpoints all frames in the log file and syncs the
+database file. This mode blocks new database writers while it is pending,
+but new database readers are allowed to continue unimpeded.</p>
+
+<p><dt>SQLITE_CHECKPOINT_RESTART<dd>
+This mode works the same way as SQLITE_CHECKPOINT_FULL with the addition
+that after checkpointing the log file it blocks (calls the
+<a href="../c3ref/busy_handler.html">busy-handler callback</a>)
+until all readers are reading from the database file only. This ensures
+that the next writer will restart the log file from the beginning.
+Like SQLITE_CHECKPOINT_FULL, this mode blocks new
+database writer attempts while it is pending, but does not impede readers.</p>
+
+<p><dt>SQLITE_CHECKPOINT_TRUNCATE<dd>
+This mode works the same way as SQLITE_CHECKPOINT_RESTART with the
+addition that it also truncates the log file to zero bytes just prior
+to a successful return.
+</dl></p>
+
+<p>If pnLog is not NULL, then *pnLog is set to the total number of frames in
+the log file or to -1 if the checkpoint could not run because
+of an error or because the database is not in <a href="../wal.html">WAL mode</a>. If pnCkpt is not
+NULL,then *pnCkpt is set to the total number of checkpointed frames in the
+log file (including any that were already checkpointed before the function
+was called) or to -1 if the checkpoint could not run due to an error or
+because the database is not in WAL mode. Note that upon successful
+completion of an SQLITE_CHECKPOINT_TRUNCATE, the log file will have been
+truncated to zero bytes and so both *pnLog and *pnCkpt will be set to zero.</p>
+
+<p>All calls obtain an exclusive "checkpoint" lock on the database file. If
+any other process is running a checkpoint operation at the same time, the
+lock cannot be obtained and SQLITE_BUSY is returned. Even if there is a
+busy-handler configured, it will not be invoked in this case.</p>
+
+<p>The SQLITE_CHECKPOINT_FULL, RESTART and TRUNCATE modes also obtain the
+exclusive "writer" lock on the database file. If the writer lock cannot be
+obtained immediately, and a busy-handler is configured, it is invoked and
+the writer lock retried until either the busy-handler returns 0 or the lock
+is successfully obtained. The busy-handler is also invoked while waiting for
+database readers as described above. If the busy-handler returns 0 before
+the writer lock is obtained or while waiting for database readers, the
+checkpoint operation proceeds from that point in the same way as
+SQLITE_CHECKPOINT_PASSIVE - checkpointing as many frames as possible
+without blocking any further. SQLITE_BUSY is returned in this case.</p>
+
+<p>If parameter zDb is NULL or points to a zero length string, then the
+specified operation is attempted on all WAL databases <a href="../lang_attach.html">attached</a> to
+<a href="../c3ref/sqlite3.html">database connection</a> db.  In this case the
+values written to output parameters *pnLog and *pnCkpt are undefined. If
+an SQLITE_BUSY error is encountered when processing one or more of the
+attached WAL databases, the operation is still attempted on any remaining
+attached databases and SQLITE_BUSY is returned at the end. If any other
+error occurs while processing an attached database, processing is abandoned
+and the error code is returned to the caller immediately. If no error
+(SQLITE_BUSY or otherwise) is encountered while processing the attached
+databases, SQLITE_OK is returned.</p>
+
+<p>If database zDb is the name of an attached database that is not in WAL
+mode, SQLITE_OK is returned and both *pnLog and *pnCkpt set to -1. If
+zDb is not NULL (or a zero length string) and is not the name of any
+attached database, SQLITE_ERROR is returned to the caller.</p>
+
+<p>Unless it returns SQLITE_MISUSE,
+the sqlite3_wal_checkpoint_v2() interface
+sets the error information that is queried by
+<a href="../c3ref/errcode.html">sqlite3_errcode()</a> and <a href="../c3ref/errcode.html">sqlite3_errmsg()</a>.</p>
+
+<p>The <a href="../pragma.html#pragma_wal_checkpoint">PRAGMA wal_checkpoint</a> command can be used to invoke this interface
+from SQL.
+</p><p>See also lists of
+  <a href="../c3ref/objlist.html">Objects</a>,
+  <a href="../c3ref/constlist.html">Constants</a>, and
+  <a href="../c3ref/funclist.html">Functions</a>.</p>
+