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<h1>10. Database Event Hooks</h1>
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<h2>10.5. Database Shutdown</h2>
<p>
<span class="computeroutput">DB.DBA.DBEV_SHUTDOWN()</span>
</p>
<p>
If defined, this function is called when shutting down the server,
following disconnection of all clients and making a checkpoint. When
a disconnect occurs as a result of server shutdown the DBEV_DISCONNECT hook is not called
and this function is expected to perform any logout processing.
The rationale is that all disconnect hooks would be called at the same time,
creating likely deadlocks, resource contention and there could be no
guarantee of time consumed by them or of even whether
they would terminate at all.
</p>
<p>
The shutdown will do a checkpoint before calling this hook. This checkpoint
will terminate all transactions with a deadlock state. If transactions
contain automatic retries, etc..., we cannot guarantee that all activity would
have terminated when this hook starts. However, the hook function can try
</p>
<div>
<pre class="programlisting">
txn_killall (6);
rollback work;
</pre>
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<p>
to signal an error on all other transactions to prompt them to
terminate. Again, this is not a sure-fire termination since this
could be handled by procedures.
</p>
<p>
When this hook returns the server commits the transaction
in which this was running and exits regardless of any lingering
activity. There is no hard time limit for this function.
Killing the process during this function has no specific ill effect, besides losing
uncommitted work by said function.
</p>
<p>
Result sets are prohibited, return values are discarded, errors are logged
but not otherwise processed.
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<div class="exampletitle">The Shutdown Hook</div>
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<pre class="programlisting">
create procedure DB.DBA.DBEV_SHUTDOWN ()
{
dbg_obj_print (' server shut down.');
update security_log set sl_logged_out = now () where sl_logged_out is null;
}
</pre>
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This just marks all open connections to be disconnected at the current time.
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