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Don't search for volatile expr in find_em_expr_usable_for_sorting_rel

While prepare_sort_from_pathkeys has to be concerned about matching upa volatile expression to the proper tlist entry, we don't need to dothat in find_em_expr_usable_for_sorting_rel becausee such a sort willhave to be postponed anyway.Author: James ColemanReviewed-by: Tomas VondraBackpatch-through: 13Discussion:https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs%3DhC0mSksZC%3DH5M8LSchj5e5OxpTAg%40mail.gmail.com

1 parentd016763 commitaa97890Copy full SHA for aa97890

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src/backend/optimizer/path
- equivclass.c

1 file changed

-23

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`‎src/backend/optimizer/path/equivclass.c`

Lines changed: 5 additions & 23 deletions

Original file line number	Diff line number	Diff line change
`@@ -813,8 +813,6 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo root, EquivalenceClass ec,`
`813`	`813`	`{`
`814`	`814`	`EquivalenceMember*em=lfirst(lc_em);`
`815`	`815`	`Expr*em_expr=em->em_expr;`
`816`		`-PathTarget*target=rel->reltarget;`
`817`		`-ListCell*lc_target_expr;`
`818`	`816`
`819`	`817`	`/*`
`820`	`818`	`* We shouldn't be trying to sort by an equivalence class that`
`@@ -848,30 +846,14 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo root, EquivalenceClass ec,`
`848`	`846`	`* As long as the expression isn't volatile then`
`849`	`847`	`* prepare_sort_from_pathkeys is able to generate a new target entry,`
`850`	`848`	`* so there's no need to verify that one already exists.`
	`849`	`+ *`
	`850`	`+ * While prepare_sort_from_pathkeys has to be concerned about matching`
	`851`	`+ * up a volatile expression to the proper tlist entry, it doesn't seem`
	`852`	`+ * valuable here to expend the work trying to find a match in the`
	`853`	`+ * target's exprs since such a sort will have to be postponed anyway.`
`851`	`854`	`*/`
`852`	`855`	`if (!ec->ec_has_volatile)`
`853`	`856`	`returnem->em_expr;`
`854`		`-`
`855`		`-/*`
`856`		`- * If, however, it's volatile, we have to verify that the`
`857`		`- * equivalence member's expr is already generated in the`
`858`		`- * relation's target (we do strip relabels first from both`
`859`		`- * expressions, which is cheap and might allow us to match`
`860`		`- * more expressions).`
`861`		`- */`
`862`		`-while (em_expr&&IsA(em_expr,RelabelType))`
`863`		`-em_expr= ((RelabelType*)em_expr)->arg;`
`864`		`-`
`865`		`-foreach(lc_target_expr,target->exprs)`
`866`		`-{`
`867`		`-Expr*target_expr=lfirst(lc_target_expr);`
`868`		`-`
`869`		`-while (target_expr&&IsA(target_expr,RelabelType))`
`870`		`-target_expr= ((RelabelType*)target_expr)->arg;`
`871`		`-`
`872`		`-if (equal(target_expr,em_expr))`
`873`		`-returnem->em_expr;`
`874`		`-}`
`875`	`857`	`}`
`876`	`858`
`877`	`859`	`/* We didn't find any suitable equivalence class expression */`

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`‎src/backend/optimizer/path/equivclass.c`

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