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Refactor heap_page_prune so that instead of changing item states on-the-fly,

it accumulates the set of changes to be made and then applies them. It hadto accumulate the set of changes anyway to prepare a WAL record for thepruning action, so this isn't an enormous change; the only new complexity isto not doubly mark tuples that are visited twice in the scan. The mainadvantage is that we can substantially reduce the scope of the criticalsection in which the changes are applied, thus avoiding PANIC in foreseeablecases like running out of memory in inval.c. A nice secondary advantage isthat it is now far clearer that WAL replay will actually do the same thingthat the original pruning did.This commit doesn't do anything about the open problem thatCacheInvalidateHeapTuple doesn't have the right semantics for a CTID changecaused by collapsing out a redirect pointer. But whatever we do about that,it'll be a good idea to not do it inside a critical section.

1 parentcc05d05 commit6f10eb2Copy full SHA for 6f10eb2

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3 files changed

+294

-197

lines changed

src
- backend/access/heap
  - heapam.c
  - pruneheap.c
- include/access
  - heapam.h

3 files changed

+294

-197

lines changed

`‎src/backend/access/heap/heapam.c`

Lines changed: 19 additions & 54 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.250 2008/03/04 19:54:06 tgl Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.251 2008/03/08 21:57:59 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*`
`14`	`14`	`* INTERFACE ROUTINES`
`@@ -3967,11 +3967,13 @@ heap_xlog_clean(XLogRecPtr lsn, XLogRecord *record, bool clean_move)`
`3967`	`3967`	`Relationreln;`
`3968`	`3968`	`Bufferbuffer;`
`3969`	`3969`	`Pagepage;`
`3970`		`-OffsetNumber*offnum;`
`3971`	`3970`	`OffsetNumber*end;`
	`3971`	`+OffsetNumber*redirected;`
	`3972`	`+OffsetNumber*nowdead;`
	`3973`	`+OffsetNumber*nowunused;`
`3972`	`3974`	`intnredirected;`
`3973`	`3975`	`intndead;`
`3974`		`-inti;`
	`3976`	`+intnunused;`
`3975`	`3977`
`3976`	`3978`	`if (record->xl_info&XLR_BKP_BLOCK_1)`
`3977`	`3979`	`return;`
`@@ -3990,61 +3992,24 @@ heap_xlog_clean(XLogRecPtr lsn, XLogRecord *record, bool clean_move)`
`3990`	`3992`
`3991`	`3993`	`nredirected=xlrec->nredirected;`
`3992`	`3994`	`ndead=xlrec->ndead;`
`3993`		`-offnum= (OffsetNumber) ((char)xlrec+SizeOfHeapClean);`
`3994`	`3995`	`end= (OffsetNumber) ((char)xlrec+record->xl_len);`
`3995`		`-`
`3996`		`-/* Update all redirected or moved line pointers */`
`3997`		`-for (i=0;i<nredirected;i++)`
`3998`		`-{`
`3999`		`-OffsetNumberfromoff=*offnum++;`
`4000`		`-OffsetNumbertooff=*offnum++;`
`4001`		`-ItemIdfromlp=PageGetItemId(page,fromoff);`
`4002`		`-`
`4003`		`-if (clean_move)`
`4004`		`-{`
`4005`		`-/* Physically move the "to" item to the "from" slot */`
`4006`		`-ItemIdtolp=PageGetItemId(page,tooff);`
`4007`		`-HeapTupleHeaderhtup;`
`4008`		`-`
`4009`		`-fromlp=tolp;`
`4010`		`-ItemIdSetUnused(tolp);`
`4011`		`-`
`4012`		`-/* We also have to clear the tuple's heap-only bit */`
`4013`		`-Assert(ItemIdIsNormal(fromlp));`
`4014`		`-htup= (HeapTupleHeader)PageGetItem(page,fromlp);`
`4015`		`-Assert(HeapTupleHeaderIsHeapOnly(htup));`
`4016`		`-HeapTupleHeaderClearHeapOnly(htup);`
`4017`		`-}`
`4018`		`-else`
`4019`		`-{`
`4020`		`-/* Just insert a REDIRECT link at fromoff */`
`4021`		`-ItemIdSetRedirect(fromlp,tooff);`
`4022`		`-}`
`4023`		`-}`
`4024`		`-`
`4025`		`-/* Update all now-dead line pointers */`
`4026`		`-for (i=0;i<ndead;i++)`
`4027`		`-{`
`4028`		`-OffsetNumberoff=*offnum++;`
`4029`		`-ItemIdlp=PageGetItemId(page,off);`
`4030`		`-`
`4031`		`-ItemIdSetDead(lp);`
`4032`		`-}`
`4033`		`-`
`4034`		`-/* Update all now-unused line pointers */`
`4035`		`-while (offnum<end)`
`4036`		`-{`
`4037`		`-OffsetNumberoff=*offnum++;`
`4038`		`-ItemIdlp=PageGetItemId(page,off);`
`4039`		`-`
`4040`		`-ItemIdSetUnused(lp);`
`4041`		`-}`
	`3996`	`+redirected= (OffsetNumber) ((char)xlrec+SizeOfHeapClean);`
	`3997`	`+nowdead=redirected+ (nredirected*2);`
	`3998`	`+nowunused=nowdead+ndead;`
	`3999`	`+nunused= (end-nowunused);`
	`4000`	`+Assert(nunused >=0);`
	`4001`	`+`
	`4002`	`+/* Update all item pointers per the record, and repair fragmentation */`
	`4003`	`+heap_page_prune_execute(reln,buffer,`
	`4004`	`+redirected,nredirected,`
	`4005`	`+nowdead,ndead,`
	`4006`	`+nowunused,nunused,`
	`4007`	`+clean_move);`
`4042`	`4008`
`4043`	`4009`	`/*`
`4044`		`- *Finally, repair any fragmentation, and update the page'shint bit about`
`4045`		`- *whether it has free pointers.`
	`4010`	`+ *Note: we don't worry about updating the page'sprunability hints.`
	`4011`	`+ *At worst this will cause an extra prune cycle to occur soon.`
`4046`	`4012`	`*/`
`4047`		`-PageRepairFragmentation(page);`
`4048`	`4013`
`4049`	`4014`	`PageSetLSN(page,lsn);`
`4050`	`4015`	`PageSetTLI(page,ThisTimeLineID);`

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Commit6f10eb2

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3 files changed

`‎src/backend/access/heap/heapam.c`

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