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When pushing down a join to a foreign server, postgres_fdw constructs an alternative plan to be used for any EvalPlanQual rechecks that prove to be necessary. This plan is stored as the outer subplan of the Foreign Scan implementing the pushed-down join. Previously, this alternative plan could have a different nominal sort ordering than its parent, which seemed OK since there will only be one tuple per base table anyway in the case of an EvalPlanQual recheck. Actually, though, it caused a problem if that path was used as a building block for the EvalPlanQual recheck plan of a higher-level foreign join, because we could end up with a merge join one of whose inputs was not labelled with the correct sort order. Repair by injecting an extra Sort node into the EvalPlanQual recheck plan whenever it would otherwise fail to be sorted at least as well as its parent Foreign Scan. Report by Jeff Janes. Patch by me, reviewed by Tom Lane, who also provided the test case and comment text. Discussion: http://postgr.es/m/CAMkU=1y2G8VOVBHv3iXU2TMAj7-RyBFFW1uhkr5sm9LQ2=X35g@mail.gmail.com
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.