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Add some additional core functions to support join pushdown for FDWs.

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GetExistingLocalJoinPath() is useful for handling EvalPlanQual rechecks
properly, and GetUserMappingById() is needed to make sure you're using
the right credentials.

Shigeru Hanada, Etsuro Fujita, Ashutosh Bapat, Robert Haas
This commit is contained in:
Robert Haas
2016-02-04 17:05:09 -05:00
parent c1772ad922
commit a104a017fc
4 changed files with 196 additions and 2 deletions
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32
doc/src/sgml/fdwhandler.sgml
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@ -341,6 +341,21 @@ GetForeignJoinPaths (PlannerInfo *root,
See <xref linkend="fdw-planning"> for additional information.
</para>
<para>
<programlisting>
void
GetExistingLocalJoinPath(RelOptInfo *joinrel)
</programlisting>
The function returns copy of a local join path, which can be converted
into an alternative local join plan, which may be useful when
implementing a <literal>RecheckForeignScan</> method. The function
searches for a parallel-safe, unparameterized path in the
<literal>pathlist</> of given <literal>joinrel</>. If it does not find
such a path, it returns NULL, in which case a foreign data wrapper may
build the local path by itself or may choose not to create access paths
for that join.
</para>
</sect2>
<sect2 id="fdw-callbacks-update">
@ -794,6 +809,9 @@ RecheckForeignScan (ForeignScanState *node, TupleTableSlot *slot);
can be executed and the resulting tuple can be stored in the slot.
This plan need not be efficient since no base table will return more
than one row; for example, it may implement all joins as nested loops.
<literal>GetExistingLocalJoinPath</> may be used to search existing paths
for a suitable local join path, which can be used as the alternative
local join plan.
</para>
</sect2>
@ -1069,6 +1087,20 @@ GetForeignTable(Oid relid);
<para>
<programlisting>
UserMapping *
GetUserMappingById(Oid umid);
</programlisting>
This function returns the <structname>UserMapping</structname> object for
the given user mapping OID. The OID of a user mapping for a foreign scan
is available in the <structname>RelOptInfo</structname>.
If there is no mapping for the OID, this function will throw an error.
A <structname>UserMapping</structname> object contains properties of the
user mapping (see <filename>foreign/foreign.h</filename> for details).
</para>
<para>
<programlisting>
List *
GetForeignColumnOptions(Oid relid, AttrNumber attnum);
</programlisting>