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Clarify the relationship between find_em_expr_usable_for_sorting_rel andprepare_sort_from_pathkeys, i.e. what restrictions need to be sharedbetween those two places.Author: James ColemanReviewed-by: Tomas VondraBackpatch-through: 13Discussion:https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs%3DhC0mSksZC%3DH5M8LSchj5e5OxpTAg%40mail.gmail.com

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Lines changed: 5 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -798,9 +798,11 @@ find_em_expr_for_rel(EquivalenceClass ec, RelOptInfo rel)`
`798`	`798`	`}`
`799`	`799`
`800`	`800`	`/*`
`801`		`- * Find an equivalence class member expression that can be safely used by a`
`802`		`- * sort node on top of the provided relation. The rules here must match those`
`803`		`- * applied in prepare_sort_from_pathkeys.`
	`801`	`+ * Find an equivalence class member expression that can be safely used to build`
	`802`	`+ * a sort node using the provided relation. The rules are a subset of those`
	`803`	`+ * applied in prepare_sort_from_pathkeys since that function deals with sorts`
	`804`	`+ * that must be delayed until the last stages of query execution, while here`
	`805`	`+ * we only care about proactive sorts.`
`804`	`806`	`*/`
`805`	`807`	`Expr*`
`806`	`808`	`find_em_expr_usable_for_sorting_rel(PlannerInforoot,EquivalenceClassec,`

Lines changed: 3 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -5850,6 +5850,9 @@ make_incrementalsort(Plan *lefttree, int numCols, int nPresortedCols,`
`5850`	`5850`	`*`
`5851`	`5851`	`* Returns the node which is to be the input to the Sort (either lefttree,`
`5852`	`5852`	`* or a Result stacked atop lefttree).`
	`5853`	`+ *`
	`5854`	`+ * Note: Restrictions on what expressions are safely sortable may also need to`
	`5855`	`+ * be added to find_em_expr_usable_for_sorting_rel.`
`5853`	`5856`	`*/`
`5854`	`5857`	`staticPlan*`
`5855`	`5858`	`prepare_sort_from_pathkeys(Planlefttree,Listpathkeys,`

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