Andres Freund 623a9ba79b snapshot scalability: cache snapshots using a xact completion counter. ... Previous commits made it faster/more scalable to compute snapshots. But not building a snapshot is still faster. Now that GetSnapshotData() does not maintain RecentGlobal* anymore, that is actually not too hard: This commit introduces xactCompletionCount, which tracks the number of top-level transactions with xids (i.e. which may have modified the database) that completed in some form since the start of the server. We can avoid rebuilding the snapshot's contents whenever the current xactCompletionCount is the same as it was when the snapshot was originally built. Currently this check happens while holding ProcArrayLock. While it's likely possible to perform the check without acquiring ProcArrayLock, it seems better to do that separately / later, some careful analysis is required. Even with the lock this is a significant win on its own. On a smaller two socket machine this gains another ~1.03x, on a larger machine the effect is roughly double (earlier patch version tested though). If we were able to safely avoid the lock there'd be another significant gain on top of that. Author: Andres Freund <andres@anarazel.de> Reviewed-By: Robert Haas <robertmhaas@gmail.com> Reviewed-By: Thomas Munro <thomas.munro@gmail.com> Reviewed-By: David Rowley <dgrowleyml@gmail.com> Discussion: https://postgr.es/m/20200301083601.ews6hz5dduc3w2se@alap3.anarazel.de		2020-08-17 21:08:30 -07:00
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combocid.c	Update copyrights for 2020	2020-01-01 12:21:45 -05:00
Makefile	Split all OBJS style lines in makefiles into one-line-per-entry style.	2019-11-05 14:41:07 -08:00
snapmgr.c	snapshot scalability: cache snapshots using a xact completion counter.	2020-08-17 21:08:30 -07:00