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Make tbm_add_tuples more efficient by caching the last acccessed page.

When adding a large number of tuples to a TID bitmap usingtbm_add_tuples() sometimes a lot of time was spent looking up a page'sentry in the bitmap's internal hashtable.Improve efficiency by caching the last accessed page, while iteratingover the passed in tuples, hoping consecutive tuples will often be onthe same page. In many cases that's a good bet, and in the rest theadded overhead isn't big.Discussion: 54479A85.8060309@sigaev.ruAuthor: Teodor SigaevReviewed-By: David Rowley

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src/backend/nodes
- tidbitmap.c

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+18

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lines changed

`‎src/backend/nodes/tidbitmap.c`

Lines changed: 18 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -268,25 +268,33 @@ void`
`268`	`268`	`tbm_add_tuples(TIDBitmap*tbm,constItemPointertids,intntids,`
`269`	`269`	`boolrecheck)`
`270`	`270`	`{`
`271`		`-inti;`
	`271`	`+inti;`
	`272`	`+PagetableEntry*page=NULL;`
`272`	`273`
`273`	`274`	`Assert(!tbm->iterating);`
`274`	`275`	`for (i=0;i<ntids;i++)`
`275`	`276`	`{`
`276`	`277`	`BlockNumberblk=ItemPointerGetBlockNumber(tids+i);`
`277`	`278`	`OffsetNumberoff=ItemPointerGetOffsetNumber(tids+i);`
`278`		`-PagetableEntry*page;`
`279`	`279`	`intwordnum,`
`280`	`280`	`bitnum;`
`281`	`281`
`282`	`282`	`/* safety check to ensure we don't overrun bit array bounds */`
`283`	`283`	`if (off<1\|\|off>MAX_TUPLES_PER_PAGE)`
`284`	`284`	`elog(ERROR,"tuple offset out of range: %u",off);`
`285`	`285`
`286`		`-if (tbm_page_is_lossy(tbm,blk))`
`287`		`-continue;/* whole page is already marked */`
`288`		`-`
`289`		`-page=tbm_get_pageentry(tbm,blk);`
	`286`	`+if (page==NULL\|\|page->blockno!=blk)`
	`287`	`+{`
	`288`	`+if (tbm_page_is_lossy(tbm,blk))`
	`289`	`+continue;/* whole page is already marked */`
	`290`	`+`
	`291`	`+/*`
	`292`	`+ * Cache this page as it's quite likely that we'll see the same`
	`293`	`+ * page again in the next iteration. This will save having to`
	`294`	`+ * lookup the page in the hashtable again.`
	`295`	`+ */`
	`296`	`+page=tbm_get_pageentry(tbm,blk);`
	`297`	`+}`
`290`	`298`
`291`	`299`	`if (page->ischunk)`
`292`	`300`	`{`
`@@ -303,7 +311,11 @@ tbm_add_tuples(TIDBitmap *tbm, const ItemPointer tids, int ntids,`
`303`	`311`	`page->recheck \|=recheck;`
`304`	`312`
`305`	`313`	`if (tbm->nentries>tbm->maxentries)`
	`314`	`+{`
`306`	`315`	`tbm_lossify(tbm);`
	`316`	`+/* Cached page could become lossy or freed */`
	`317`	`+page=NULL;`
	`318`	`+}`
`307`	`319`	`}`
`308`	`320`	`}`
`309`	`321`

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`‎src/backend/nodes/tidbitmap.c`

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