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<title>Berkeley DB Reference Guide: Database verification and salvage</title>
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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></b></td>
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<p align=center><b>Database verification and salvage</b></p>
<p>The <a href="../../api_c/db_verify.html">DB-&gt;verify</a> method verifies that a file, and any databases it may
contain, are uncorrupted.  In addition, the method may optionally be
called with a file stream argument to which all key/data pairs found in
the database are output.  There are two modes for finding key/data pairs
to be output:</p>
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<p><li>If the <a href="../../api_c/db_verify.html#DB_SALVAGE">DB_SALVAGE</a> flag is specified, the key/data pairs in the
database are output.  When run in this mode, the database is assumed to
be largely uncorrupted. For example, the <a href="../../api_c/db_verify.html">DB-&gt;verify</a> method will
search for pages that are no longer linked into the database, and will
output key/data pairs from such pages.  However, key/data items that
have been marked as deleted in the database will not be output, as the
page structures are generally trusted in this mode.
<p><li>If both the <a href="../../api_c/db_verify.html#DB_SALVAGE">DB_SALVAGE</a> and <a href="../../api_c/db_verify.html#DB_AGGRESSIVE">DB_AGGRESSIVE</a> flags are
specified, all possible key/data pairs are output.  When run in this mode,
the database is assumed to be seriously corrupted.  For example, key/data
pairs that have been deleted will re-appear in the output.  In addition,
because pages may have been subsequently reused and modified during
normal database operations after the key/data pairs were deleted, it is
not uncommon for apparently corrupted key/data pairs to be output in this
mode, even when there is no corruption in the underlying database.  The
output will almost always have to be edited by hand or other means before
the data is ready for reload into another database.  We recommend that
<a href="../../api_c/db_verify.html#DB_SALVAGE">DB_SALVAGE</a> be tried first, and <a href="../../api_c/db_verify.html#DB_AGGRESSIVE">DB_AGGRESSIVE</a> only tried
if the output from that first attempt is obviously missing data items or
the data is sufficiently valuable that human review of the output is
preferable to any kind of data loss.
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