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Allow custom and foreign scans to have shutdown callbacks.

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This is expected to be useful mostly when performing such scans in
parallel, because in that case it allows (in combination with commit
acf555bc53) nodes below a Gather to get
control just before the DSM segment goes away.

KaiGai Kohei, except that I rewrote the documentation.  Reviewed by
Claudio Freire.

Discussion: http://postgr.es/m/CADyhKSXJK0jUJ8rWv4AmKDhsUh124_rEn39eqgfC5D8fu6xVuw@mail.gmail.com
This commit is contained in:
Robert Haas
2017-02-26 13:36:49 +05:30
parent 285ca26132
commit a315b967cc
9 changed files with 63 additions and 0 deletions
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13
doc/src/sgml/custom-scan.sgml
View File

@ -340,6 +340,19 @@ void (*InitializeWorkerCustomScan) (CustomScanState *node,
<para>
<programlisting>
void (*ShutdownCustomScan) (CustomScanState *node);
</programlisting>
Release resources when it is anticipated the node will not be executed
to completion. This is not called in all cases; sometimes,
<literal>EndCustomScan</> may be called without this function having
been called first. Since the DSM segment used by parallel query is
destroyed just after this callback is invoked, custom scan providers that
wish to take some action before the DSM segment goes away should implement
this method.
</para>
<para>
<programlisting>
void (*ExplainCustomScan) (CustomScanState *node,
List *ancestors,
ExplainState *es);

14
doc/src/sgml/fdwhandler.sgml
View File

@ -1254,6 +1254,20 @@ InitializeWorkerForeignScan(ForeignScanState *node, shm_toc *toc,
This callback is optional, and needs only be supplied if this
custom path supports parallel execution.
</para>
<para>
<programlisting>
void
ShutdownForeignScan(ForeignScanState *node);
</programlisting>
Release resources when it is anticipated the node will not be executed
to completion. This is not called in all cases; sometimes,
<literal>EndForeignScan</> may be called without this function having
been called first. Since the DSM segment used by parallel query is
destroyed just after this callback is invoked, foreign data wrappers that
wish to take some action before the DSM segment goes away should implement
this method.
</para>
</sect2>
</sect1>