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Suppress unnecessary explicit sorting for EPQ mergejoin path
When building a ForeignPath for a joinrel, if there's a possibility that EvalPlanQual will be executed, we must identify a suitable path for EPQ checks. If the outer or inner path of the chosen path is a ForeignPath representing a pushed-down join, we replace it with its fdw_outerpath to ensure that the EPQ check path consists entirely of local joins. If the chosen path is a MergePath, and its outer or inner path is a ForeignPath that is not already well enough ordered, the MergePath will have non-NIL outersortkeys or innersortkeys indicating the desired ordering to be created by an explicit Sort node. If we then replace the outer or inner path with its corresponding fdw_outerpath, and that path is already sufficiently ordered, we end up in an inconsistent state: the MergePath has non-NIL outersortkeys or innersortkeys, and its input path is already properly ordered. This inconsistency can result in an Assert failure or the addition of a redundant Sort node. To fix, check if the new outer or inner path of a MergePath is already properly sorted, and set its outersortkeys or innersortkeys to NIL if so. Bug: #18902 Reported-by: Nikita Kalinin <n.kalinin@postgrespro.ru> Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tender Wang <tndrwang@gmail.com> Discussion: https://postgr.es/m/18902-71c1bed2b9f7c46f@postgresql.org
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@ -22,6 +22,7 @@
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#include "foreign/foreign.h"
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#include "funcapi.h"
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#include "miscadmin.h"
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#include "optimizer/paths.h"
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#include "tcop/tcopprot.h"
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#include "utils/builtins.h"
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#include "utils/memutils.h"
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@ -808,7 +809,23 @@ GetExistingLocalJoinPath(RelOptInfo *joinrel)
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foreign_path = (ForeignPath *) joinpath->outerjoinpath;
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if (IS_JOIN_REL(foreign_path->path.parent))
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{
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joinpath->outerjoinpath = foreign_path->fdw_outerpath;
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if (joinpath->path.pathtype == T_MergeJoin)
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{
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MergePath *merge_path = (MergePath *) joinpath;
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/*
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* If the new outer path is already well enough ordered
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* for the mergejoin, we can skip doing an explicit sort.
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*/
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if (merge_path->outersortkeys &&
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pathkeys_contained_in(merge_path->outersortkeys,
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joinpath->outerjoinpath->pathkeys))
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merge_path->outersortkeys = NIL;
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}
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}
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}
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if (IsA(joinpath->innerjoinpath, ForeignPath))
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@ -817,7 +834,23 @@ GetExistingLocalJoinPath(RelOptInfo *joinrel)
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foreign_path = (ForeignPath *) joinpath->innerjoinpath;
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if (IS_JOIN_REL(foreign_path->path.parent))
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{
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joinpath->innerjoinpath = foreign_path->fdw_outerpath;
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if (joinpath->path.pathtype == T_MergeJoin)
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{
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MergePath *merge_path = (MergePath *) joinpath;
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/*
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* If the new inner path is already well enough ordered
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* for the mergejoin, we can skip doing an explicit sort.
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*/
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if (merge_path->innersortkeys &&
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pathkeys_contained_in(merge_path->innersortkeys,
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joinpath->innerjoinpath->pathkeys))
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merge_path->innersortkeys = NIL;
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}
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}
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}
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return (Path *) joinpath;
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