Peter Geoghegan 1de58df4fe Add page-level freezing to VACUUM. ... Teach VACUUM to decide on whether or not to trigger freezing at the level of whole heap pages. Individual XIDs and MXIDs fields from tuple headers now trigger freezing of whole pages, rather than independently triggering freezing of each individual tuple header field. Managing the cost of freezing over time now significantly influences when and how VACUUM freezes. The overall amount of WAL written is the single most important freezing related cost, in general. Freezing each page's tuples together in batch allows VACUUM to take full advantage of the freeze plan WAL deduplication optimization added by commit 9e540599. Also teach VACUUM to trigger page-level freezing whenever it detects that heap pruning generated an FPI. We'll have already written a large amount of WAL just to do that much, so it's very likely a good idea to get freezing out of the way for the page early. This only happens in cases where it will directly lead to marking the page all-frozen in the visibility map. In most cases "freezing a page" removes all XIDs < OldestXmin, and all MXIDs < OldestMxact. It doesn't quite work that way in certain rare cases involving MultiXacts, though. It is convenient to define "freeze the page" in a way that gives FreezeMultiXactId the leeway to put off the work of processing an individual tuple's xmax whenever it happens to be a MultiXactId that would require an expensive second pass to process aggressively (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 require expensive second pass processing. This avoids regressions related to processing 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		2022-12-28 08:50:47 -08:00
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src	Add page-level freezing to VACUUM.	2022-12-28 08:50:47 -08:00
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