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Add page-level freezing to VACUUM.

Teach VACUUM to decide on whether or not to trigger freezing at thelevel of whole heap pages. Individual XIDs and MXIDs fields from tupleheaders now trigger freezing of whole pages, rather than independentlytriggering freezing of each individual tuple header field.Managing the cost of freezing over time now significantly influenceswhen and how VACUUM freezes. The overall amount of WAL written is thesingle most important freezing related cost, in general. Freezing eachpage's tuples together in batch allows VACUUM to take full advantage ofthe freeze plan WAL deduplication optimization added by commit9e54059.Also teach VACUUM to trigger page-level freezing whenever it detectsthat heap pruning generated an FPI. We'll have already written a largeamount of WAL just to do that much, so it's very likely a good idea toget freezing out of the way for the page early. This only happens incases where it will directly lead to marking the page all-frozen in thevisibility map.In most cases "freezing a page" removes all XIDs < OldestXmin, and allMXIDs < OldestMxact. It doesn't quite work that way in certain rarecases involving MultiXacts, though. It is convenient to define "freezethe page" in a way that gives FreezeMultiXactId the leeway to put offthe work of processing an individual tuple's xmax whenever it happens tobe a MultiXactId that would require an expensive second pass to processaggressively (allocating a new multi is especially worth avoiding here).FreezeMultiXactId is eager when processing is cheap (as it usually is),and lazy in the event of an individual multi that happens to requireexpensive second pass processing. This avoids regressions related toprocessing of multis that page-level freezing might otherwise cause.Author: Peter Geoghegan <pg@bowt.ie>Reviewed-By: Jeff Davis <pgsql@j-davis.com>Reviewed-By: Andres Freund <andres@anarazel.de>Discussion:https://postgr.es/m/CAH2-WzkFok_6EAHuK39GaW4FjEFQsY=3J0AAd6FXk93u-Xq3Fg@mail.gmail.com

1 parent7a05425 commit1de58dfCopy full SHA for 1de58df

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doc/src/sgml
- config.sgml
src
- backend/access/heap
  - heapam.c
  - vacuumlazy.c
- include/access
  - heapam.h

4 files changed

+463

-297

lines changed

`‎doc/src/sgml/config.sgml`

Lines changed: 5 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -9194,9 +9194,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;`
`9194`	`9194`	`</term>`
`9195`	`9195`	`<listitem>`
`9196`	`9196`	`<para>`
`9197`		`- Specifies the cutoff age (in transactions) that <command>VACUUM</command>`
`9198`		`- should use to decide whether to freeze row versions`
`9199`		`-while scanning a table.`
	`9197`	`+ Specifies the cutoff age (in transactions) that`
	`9198`	`+<command>VACUUM</command>should use to decide whether to`
	`9199`	`+trigger freezing of pages that have an older XID.`
`9200`	`9200`	`The default is 50 million transactions. Although`
`9201`	`9201`	`users can set this value anywhere from zero to one billion,`
`9202`	`9202`	`<command>VACUUM</command> will silently limit the effective value to half`
`@@ -9274,9 +9274,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;`
`9274`	`9274`	`<listitem>`
`9275`	`9275`	`<para>`
`9276`	`9276`	`Specifies the cutoff age (in multixacts) that <command>VACUUM</command>`
`9277`		`- should use to decide whether to replace multixact IDs with a newer`
`9278`		`- transaction ID or multixact ID while scanning a table. The default`
`9279`		`- is 5 million multixacts.`
	`9277`	`+ should use to decide whether to trigger freezing of pages with`
	`9278`	`+ an older multixact ID. The default is 5 million multixacts.`
`9280`	`9279`	`Although users can set this value anywhere from zero to one billion,`
`9281`	`9280`	`<command>VACUUM</command> will silently limit the effective value to half`
`9282`	`9281`	`the value of <xref linkend="guc-autovacuum-multixact-freeze-max-age"/>,`

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Commit1de58df

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`‎doc/src/sgml/config.sgml`

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