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Diffstat (limited to 'doc/src/sgml/fdwhandler.sgml')
| -rw-r--r-- | doc/src/sgml/fdwhandler.sgml | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml index 5af41318e5c..04f3c224331 100644 --- a/doc/src/sgml/fdwhandler.sgml +++ b/doc/src/sgml/fdwhandler.sgml @@ -598,6 +598,42 @@ IsForeignRelUpdatable (Relation rel); </sect2> + <sect2> + <title>FDW Routines For Remote Joins</title> + <para> +<programlisting> +void +GetForeignJoinPaths(PlannerInfo *root, + RelOptInfo *joinrel, + RelOptInfo *outerrel, + RelOptInfo *innerrel, + List *restrictlist, + JoinType jointype, + SpecialJoinInfo *sjinfo, + SemiAntiJoinFactors *semifactors, + Relids param_source_rels, + Relids extra_lateral_rels); +</programlisting> + Create possible access paths for a join of two foreign tables managed + by the same foreign data wrapper. + This optional function is called during query planning. + </para> + <para> + This function the FDW to add <structname>ForeignScan</> paths for the + supplied <literal>joinrel</>. Typically, the FDW will send the whole + join to the remote server as a single query, as performing the join + remotely rather than locally is typically much more efficient. + </para> + <para> + Since we cannot construct the slot descriptor for a remote join from + the catalogs, the FDW should set the <structfield>scanrelid</> of the + <structname>ForeignScan</> to zero and <structfield>fdw_ps_tlist</> + to an appropriate list of <structfield>TargetEntry</> nodes. + Junk entries will be ignored, but can be present for the benefit of + deparsing performed by <command>EXPLAIN</>. + </para> + </sect2> + <sect2 id="fdw-callbacks-explain"> <title>FDW Routines for <command>EXPLAIN</></title> |