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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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lines changed

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
`@@ -6025,48 +6025,6 @@ RelationIdIsInInitFile(Oid relationId)`
`6025`	`6025`	`returnRelationSupportsSysCache(relationId);`
`6026`	`6026`	`}`
`6027`	`6027`
`6028`		`-/*`
`6029`		`- * Tells whether any index for the relation is unlogged.`
`6030`		`- *`
`6031`		`- * Note: There doesn't seem to be any way to have an unlogged index attached`
`6032`		`- * to a permanent table, but it seems best to keep this general so that it`
`6033`		`- * returns sensible results even when they seem obvious (like for an unlogged`
`6034`		`- * table) and to handle possible future unlogged indexes on permanent tables.`
`6035`		`- */`
`6036`		`-bool`
`6037`		`-RelationHasUnloggedIndex(Relationrel)`
`6038`		`-{`
`6039`		`-List*indexoidlist;`
`6040`		`-ListCell*indexoidscan;`
`6041`		`-boolresult= false;`
`6042`		`-`
`6043`		`-indexoidlist=RelationGetIndexList(rel);`
`6044`		`-`
`6045`		`-foreach(indexoidscan,indexoidlist)`
`6046`		`-{`
`6047`		`-Oidindexoid=lfirst_oid(indexoidscan);`
`6048`		`-HeapTupletp;`
`6049`		`-Form_pg_classreltup;`
`6050`		`-`
`6051`		`-tp=SearchSysCache1(RELOID,ObjectIdGetDatum(indexoid));`
`6052`		`-if (!HeapTupleIsValid(tp))`
`6053`		`-elog(ERROR,"cache lookup failed for relation %u",indexoid);`
`6054`		`-reltup= (Form_pg_class)GETSTRUCT(tp);`
`6055`		`-`
`6056`		`-if (reltup->relpersistence==RELPERSISTENCE_UNLOGGED)`
`6057`		`-result= true;`
`6058`		`-`
`6059`		`-ReleaseSysCache(tp);`
`6060`		`-`
`6061`		`-if (result== true)`
`6062`		`-break;`
`6063`		`-}`
`6064`		`-`
`6065`		`-list_free(indexoidlist);`
`6066`		`-`
`6067`		`-returnresult;`
`6068`		`-}`
`6069`		`-`
`6070`	`6028`	`/*`
`6071`	`6029`	`* Invalidate (remove) the init file during commit of a transaction that`
`6072`	`6030`	`* 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
`@@ -602,7 +602,6 @@ typedef struct ViewOptions`
`602`	`602`	`/* routines in utils/cache/relcache.c */`
`603`	`603`	`externvoidRelationIncrementReferenceCount(Relationrel);`
`604`	`604`	`externvoidRelationDecrementReferenceCount(Relationrel);`
`605`		`-externboolRelationHasUnloggedIndex(Relationrel);`
`606`	`605`	`externList*RelationGetRepsetList(Relationrel);`
`607`	`606`
`608`	`607`	`#endif/* REL_H */`

`‎src/include/utils/snapmgr.h‎`

Lines changed: 0 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -40,7 +40,6 @@`
`40`	`40`	`RelationNeedsWAL(rel) \`
`41`	`41`	`&& !IsCatalogRelation(rel) \`
`42`	`42`	`&& !RelationIsAccessibleInLogicalDecoding(rel) \`
`43`		`- && !RelationHasUnloggedIndex(rel) \`
`44`	`43`	`)`
`45`	`44`
`46`	`45`	`#defineEarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))`

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Commitb9c4ccf

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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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