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Use scanned_pages to decide when to failsafe check.

Perform a failsafe check every time VACUUM's first heap scan scans afurther FAILSAFE_EVERY_PAGES pages, rather than using an approach basedon the number of physical blocks that our current blkno is from theblkno at the time of the previous failsafe check. That way VACUUM willperform a failsafe check every time it has scanned a uniform number ofpages, without it mattering when or how VACUUM skipped pages using thevisibility map.Sami Imseih, with changes to FAILSAFE_EVERY_PAGES comments added by me.Author: Sami Imseih <simseih@amazon.com>Reviewed-By: Peter Geoghegan <pg@bowt.ie>Discussion:https://postgr.es/m/401CE010-4049-4B94-9961-0B610A5D254D%40amazon.com

1 parent4ce3afb commit07eef53Copy full SHA for 07eef53

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src/backend/access/heap
- vacuumlazy.c

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`‎src/backend/access/heap/vacuumlazy.c`

Lines changed: 3 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -94,7 +94,8 @@`
`94`	`94`	`#defineBYPASS_THRESHOLD_PAGES0.02/* i.e. 2% of rel_pages */`
`95`	`95`
`96`	`96`	`/*`
`97`		`- * Perform a failsafe check every 4GB during the heap scan, approximately`
	`97`	`+ * Perform a failsafe check each time we scan another 4GB of pages.`
	`98`	`+ * (Note that this is deliberately kept to a power-of-two, usually 2^19.)`
`98`	`99`	`*/`
`99`	`100`	`#defineFAILSAFE_EVERY_PAGES \`
`100`	`101`	`((BlockNumber) (((uint64) 4 * 1024 * 1024 * 1024) / BLCKSZ))`
`@@ -821,7 +822,6 @@ lazy_scan_heap(LVRelState *vacrel)`
`821`	`822`	`BlockNumberrel_pages=vacrel->rel_pages,`
`822`	`823`	`blkno,`
`823`	`824`	`next_unskippable_block,`
`824`		`-next_failsafe_block=0,`
`825`	`825`	`next_fsm_block_to_vacuum=0;`
`826`	`826`	`VacDeadItems*dead_items=vacrel->dead_items;`
`827`	`827`	`Buffervmbuffer=InvalidBuffer;`
`@@ -895,11 +895,8 @@ lazy_scan_heap(LVRelState *vacrel)`
`895`	`895`	`* one-pass strategy, and the two-pass strategy with the index_cleanup`
`896`	`896`	`* param set to 'off'.`
`897`	`897`	`*/`
`898`		`-if (blkno-next_failsafe_block >=FAILSAFE_EVERY_PAGES)`
`899`		`-{`
	`898`	`+if (vacrel->scanned_pages %FAILSAFE_EVERY_PAGES==0)`
`900`	`899`	`lazy_check_wraparound_failsafe(vacrel);`
`901`		`-next_failsafe_block=blkno;`
`902`		`-}`
`903`	`900`
`904`	`901`	`/*`
`905`	`902`	`* Consider if we definitely have enough space to process TIDs on page`

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Commit07eef53

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`‎src/backend/access/heap/vacuumlazy.c`

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