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<h1>DbEnv::memp_sync</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
int
DbEnv::memp_sync(DbLsn *lsn);
</pre></h3>
<h1>Description</h1>
<p>The DbEnv::memp_sync method ensures that any modified pages in the pool with
log sequence numbers less than the <b>lsn</b> argument are written to
disk. If <b>lsn</b> is NULL all modified pages in the pool are
flushed.
<p>The primary purpose of the DbEnv::memp_sync function is to enable a
transaction manager to ensure, as part of a checkpoint, that all pages
modified by a certain time have been written to disk. Pages in the pool
that cannot be written back to disk immediately (e.g., that are currently
pinned) are written to disk as soon as it is possible to do so. The
expected behavior of the Berkeley DB or other transaction subsystem is to call
the DbEnv::memp_sync function and then, if the return indicates that some
pages could not be written immediately, to wait briefly and retry again
with the same log sequence number until the DbEnv::memp_sync function
returns that all pages have been written.
<p>To support the DbEnv::memp_sync functionality, it is necessary that the
pool functions know the location of the log sequence number on the page
for each file type. This location should be specified when the file is
opened using the <a href="../api_cxx/memp_fopen.html">DbMpoolFile::open</a> function. It is not required that
the log sequence number be aligned on the page in any way.
<p>The DbEnv::memp_sync method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, 0 on success, and returns <a href="../api_c/memp_fsync.html#DB_INCOMPLETE">DB_INCOMPLETE</a> if there were pages which need to be
written but which DbEnv::memp_sync was unable to write immediately.
In addition, if DbEnv::memp_sync returns success, the value of
<b>lsn</b> will be overwritten with the largest log sequence number
from any page which was written by DbEnv::memp_sync to satisfy this
request.
<h1>Errors</h1>
<p>The DbEnv::memp_sync method may fail and throw an exception or return 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 DbEnv::memp_sync function was called without logging having been
initialized in the environment.
</dl>
<p>The DbEnv::memp_sync method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the DbEnv::memp_sync method may fail and either
return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw an exception encapsulating
<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
in the same way.
<h3>Classes</h3>
<a href="../api_cxx/dbenv_class.html">DbEnv</a>, <a href="../api_cxx/mempfile_class.html">DbMpoolFile</a>
<h1>See Also</h1>
<a href="../api_cxx/env_set_mp_mmapsize.html">DbEnv::set_mp_mmapsize</a>,
<a href="../api_cxx/memp_fclose.html">DbMpoolFile::close</a>,
<a href="../api_cxx/memp_fget.html">DbMpoolFile::get</a>,
<a href="../api_cxx/memp_fopen.html">DbMpoolFile::open</a>,
<a href="../api_cxx/memp_fput.html">DbMpoolFile::put</a>,
<a href="../api_cxx/memp_fset.html">DbMpoolFile::set</a>,
<a href="../api_cxx/memp_fsync.html">DbMpoolFile::sync</a>,
<a href="../api_cxx/memp_register.html">DbEnv::memp_register</a>,
<a href="../api_cxx/memp_stat.html">DbEnv::memp_stat</a>,
<a href="../api_cxx/memp_sync.html">DbEnv::memp_sync</a>
and
<a href="../api_cxx/memp_trickle.html">DbEnv::memp_trickle</a>.
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