NotificationsYou must be signed in to change notification settings
Fork6
Star31

Commit7da8341

committed

Revive "snapshot too old" with wal_level=minimal and SET TABLESPACE.

Given a permanent relation rewritten in the current transaction, theold_snapshot_threshold mechanism assumed the relation had never beensubject to early pruning. Hence, a query could fail to report "snapshottoo old" when the rewrite followed an early truncation. ALTER TABLE SETTABLESPACE is probably the only rewrite mechanism capable of exposingthis bug. REINDEX sets indcheckxmin, avoiding the problem. CLUSTER haszeroed page LSNs since before old_snapshot_threshold existed, soold_snapshot_threshold has never cooperated with it. ALTER TABLE... SET DATA TYPE makes the table look empty to every past snapshot,which is strictly worse. Back-patch to v13, where commitc6b9204 broke this.Kyotaro Horiguchi and Noah MischDiscussion:https://postgr.es/m/20210113.160705.2225256954956139776.horikyota.ntt@gmail.com

1 parent360bd23 commit7da8341Copy full SHA for 7da8341

File tree

2 files changed

-2

lines changed

src
- backend/utils/time
  - snapmgr.c
- include/utils
  - snapmgr.h

2 files changed

-2

lines changed

`‎src/backend/utils/time/snapmgr.c`

Lines changed: 5 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -1764,7 +1764,11 @@ TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,`
`1764`	`1764`	`Assert(OldSnapshotThresholdActive());`
`1765`	`1765`	`Assert(limit_ts!=NULL&&limit_xid!=NULL);`
`1766`	`1766`
`1767`		`-if (!RelationAllowsEarlyPruning(relation))`
	`1767`	`+/*`
	`1768`	`+ * TestForOldSnapshot() assumes early pruning advances the page LSN, so we`
	`1769`	`+ * can't prune early when skipping WAL.`
	`1770`	`+ */`
	`1771`	`+if (!RelationAllowsEarlyPruning(relation)\|\| !RelationNeedsWAL(relation))`
`1768`	`1772`	`return false;`
`1769`	`1773`
`1770`	`1774`	`ts=GetSnapshotCurrentTimestamp();`

`‎src/include/utils/snapmgr.h`

Lines changed: 1 addition & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -37,7 +37,7 @@`
`37`	`37`	`*/`
`38`	`38`	`#defineRelationAllowsEarlyPruning(rel) \`
`39`	`39`	`( \`
`40`		`-RelationNeedsWAL(rel)\`
	`40`	`+ (rel)->rd_rel->relpersistence == RELPERSISTENCE_PERMANENT\`
`41`	`41`	`&& !IsCatalogRelation(rel) \`
`42`	`42`	`&& !RelationIsAccessibleInLogicalDecoding(rel) \`
`43`	`43`	`)`

0 commit comments

Comments

(0)

Movatterモバイル変換

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commit7da8341

File tree

2 files changed

2 files changed

`‎src/backend/utils/time/snapmgr.c`

`‎src/include/utils/snapmgr.h`

0 commit comments