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postgres_fdw: Avoid 'outer pathkeys do not match mergeclauses' error.
When pushing down a join to a foreign server, postgres_fdw constructsan alternative plan to be used for any EvalPlanQual rechecks thatprove to be necessary. This plan is stored as the outer subplan ofthe Foreign Scan implementing the pushed-down join. Previously, thisalternative plan could have a different nominal sort ordering than itsparent, which seemed OK since there will only be one tuple per basetable anyway in the case of an EvalPlanQual recheck. Actually,though, it caused a problem if that path was used as a building blockfor the EvalPlanQual recheck plan of a higher-level foreign join,because we could end up with a merge join one of whose inputs was notlabelled with the correct sort order. Repair by injecting an extraSort node into the EvalPlanQual recheck plan whenever it wouldotherwise fail to be sorted at least as well as its parent ForeignScan.Report by Jeff Janes. Patch by me, reviewed by Tom Lane, who alsoprovided the test case and comment text.Discussion:http://postgr.es/m/CAMkU=1y2G8VOVBHv3iXU2TMAj7-RyBFFW1uhkr5sm9LQ2=X35g@mail.gmail.com1 parentdca48d1 commit4bbf6ed
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