Horton

Re: Improving connection scalability: GetSnapshotData()

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Ian Barwick <ian.barwick@2ndquadrant.com>
Cc: Michael Paquier <michael@paquier.xyz>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Daniel Gustafsson <daniel@yesql.se>, "Jonathan S. Katz" <jkatz@postgresql.org>, Alexander Korotkov <a.korotkov@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Peter Geoghegan <pg@bowt.ie>, Bruce Momjian <bruce@momjian.us>, David Rowley <dgrowleyml@gmail.com>
Date: 2020-09-30T22:43:17Z
Lists: pgsql-hackers

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Hi,

On 2020-09-14 16:17:18 -0700, Andres Freund wrote:
> I've also included a quite heavily revised version of your test. Instead
> of using dblink I went for having a long-running psql that I feed over
> stdin. The main reason for not liking the previous version is that it
> seems fragile, with the sleep and everything.  I expanded it to cover
> 2PC is as well.
> 
> The test probably needs a bit of cleanup, wrapping some of the
> redundancy around the pump_until calls.
> 
> I think the approach of having a long running psql session is really
> useful, and probably would speed up some tests. Does anybody have a good
> idea for how to best, and without undue effort, to integrate this into
> PostgresNode.pm?  I don't really have a great idea, so I think I'd leave
> it with a local helper in the new test?

Attached is an updated version of the test (better utility function,
stricter regexes, bailing out instead of failing just the current when
psql times out).  I'm leaving it in this test for now, but it's fairly
easy to use this way, in my opinion, so it may be worth moving to
PostgresNode at some point.

Greetings,

Andres Freund

Commits

  1. Try to unbreak 021_row_visibility.pl on mingw.

  2. Fix and test snapshot behavior on standby.

  3. Fix race condition in snapshot caching when 2PC is used.

  4. snapshot scalability: cache snapshots using a xact completion counter.

  5. Fix use of wrong index in ComputeXidHorizons().

  6. Make vacuum a bit more verbose to debug BF failure.

  7. snapshot scalability: Introduce dense array of in-progress xids.

  8. snapshot scalability: Move PGXACT->vacuumFlags to ProcGlobal->vacuumFlags.

  9. snapshot scalability: Move subxact info to ProcGlobal, remove PGXACT.

  10. snapshot scalability: Move PGXACT->xmin back to PGPROC.

  11. snapshot scalability: Don't compute global horizons while building snapshots.

  12. BRIN: Handle concurrent desummarization properly

  13. Track latest completed xid as a FullTransactionId.

  14. Rename VariableCacheData.nextFullXid to nextXid.

  15. snapshot scalability: Move delayChkpt from PGXACT to PGPROC.

  16. Report progress of CREATE INDEX operations