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Avoid catalog lookups in RelationAllowsEarlyPruning().

RelationAllowsEarlyPruning() performed a catalog scan, but is usedin two contexts where that was a bad idea:1. In heap_page_prune_opt(), which runs very frequently in some large scans. This caused major performance problems in a field report that was easy to reproduce.2. In TestForOldSnapshot(), which runs while we hold a buffer content lock. It's not clear if this was guaranteed to be free of buffer deadlock risk.The check was introduced in commit2cc41ac and defended against areal problem: 9.6's hash indexes have no page LSN and so we can'tallow early pruning (ie the snapshot-too-old feature). We can removethe check from all later releases though: hash indexes are now logged,and there is no way to create UNLOGGED indexes on regular loggedtables.If a future release allows such a combination, it might need to puta similar check in place, but it'll need some more thought.Back-patch to 10.Author: Thomas MunroReviewed-by: Tom Lane, who spotted the second problemDiscussion:https://postgr.es/m/CA%2BhUKGKT8oTkp5jw_U4p0S-7UG9zsvtw_M47Y285bER6a2gD%2Bg%40mail.gmail.comDiscussion:https://postgr.es/m/CAA4eK1%2BWy%2BN4eE5zPm765h68LrkWc3Biu_8rzzi%2BOYX4j%2BiHRw%40mail.gmail.com

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3 files changed

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src
- backend/utils/cache
  - relcache.c
- include/utils
  - rel.h
  - snapmgr.h

3 files changed

-44

lines changed

`‎src/backend/utils/cache/relcache.c`

Lines changed: 0 additions & 42 deletions

Original file line number	Diff line number	Diff line change
`@@ -5941,48 +5941,6 @@ RelationIdIsInInitFile(Oid relationId)`
`5941`	`5941`	`returnRelationSupportsSysCache(relationId);`
`5942`	`5942`	`}`
`5943`	`5943`
`5944`		`-/*`
`5945`		`- * Tells whether any index for the relation is unlogged.`
`5946`		`- *`
`5947`		`- * Note: There doesn't seem to be any way to have an unlogged index attached`
`5948`		`- * to a permanent table, but it seems best to keep this general so that it`
`5949`		`- * returns sensible results even when they seem obvious (like for an unlogged`
`5950`		`- * table) and to handle possible future unlogged indexes on permanent tables.`
`5951`		`- */`
`5952`		`-bool`
`5953`		`-RelationHasUnloggedIndex(Relationrel)`
`5954`		`-{`
`5955`		`-List*indexoidlist;`
`5956`		`-ListCell*indexoidscan;`
`5957`		`-boolresult= false;`
`5958`		`-`
`5959`		`-indexoidlist=RelationGetIndexList(rel);`
`5960`		`-`
`5961`		`-foreach(indexoidscan,indexoidlist)`
`5962`		`-{`
`5963`		`-Oidindexoid=lfirst_oid(indexoidscan);`
`5964`		`-HeapTupletp;`
`5965`		`-Form_pg_classreltup;`
`5966`		`-`
`5967`		`-tp=SearchSysCache1(RELOID,ObjectIdGetDatum(indexoid));`
`5968`		`-if (!HeapTupleIsValid(tp))`
`5969`		`-elog(ERROR,"cache lookup failed for relation %u",indexoid);`
`5970`		`-reltup= (Form_pg_class)GETSTRUCT(tp);`
`5971`		`-`
`5972`		`-if (reltup->relpersistence==RELPERSISTENCE_UNLOGGED)`
`5973`		`-result= true;`
`5974`		`-`
`5975`		`-ReleaseSysCache(tp);`
`5976`		`-`
`5977`		`-if (result== true)`
`5978`		`-break;`
`5979`		`-}`
`5980`		`-`
`5981`		`-list_free(indexoidlist);`
`5982`		`-`
`5983`		`-returnresult;`
`5984`		`-}`
`5985`		`-`
`5986`	`5944`	`/*`
`5987`	`5945`	`* Invalidate (remove) the init file during commit of a transaction that`
`5988`	`5946`	`* changed one or more of the relation cache entries that are kept in the`

`‎src/include/utils/rel.h`

Lines changed: 0 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -606,7 +606,6 @@ typedef struct ViewOptions`
`606`	`606`	`/* routines in utils/cache/relcache.c */`
`607`	`607`	`externvoidRelationIncrementReferenceCount(Relationrel);`
`608`	`608`	`externvoidRelationDecrementReferenceCount(Relationrel);`
`609`		`-externboolRelationHasUnloggedIndex(Relationrel);`
`610`	`609`	`externList*RelationGetRepsetList(Relationrel);`
`611`	`610`
`612`	`611`	`#endif/* REL_H */`

`‎src/include/utils/snapmgr.h`

Lines changed: 0 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -41,7 +41,6 @@`
`41`	`41`	`RelationNeedsWAL(rel) \`
`42`	`42`	`&& !IsCatalogRelation(rel) \`
`43`	`43`	`&& !RelationIsAccessibleInLogicalDecoding(rel) \`
`44`		`- && !RelationHasUnloggedIndex(rel) \`
`45`	`44`	`)`
`46`	`45`
`47`	`46`	`#defineEarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))`

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Commit8cc6016

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3 files changed

3 files changed

`‎src/backend/utils/cache/relcache.c`

`‎src/include/utils/rel.h`

`‎src/include/utils/snapmgr.h`

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