Horton

Re: Improving connection scalability: GetSnapshotData()

Andrew Dunstan <andrew.dunstan@2ndquadrant.com>

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From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>, 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: 2020-10-01T20:00:20Z
Lists: pgsql-hackers 
On 10/1/20 2:26 PM, Andres Freund wrote:
> Hi Ian, Andrew, All,
>
> On 2020-09-30 15:43:17 -0700, Andres Freund wrote:
>> 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.
> I pushed this yesterday. Ian, thanks again for finding this and helping
> with fixing & testing.
>
>
> Unfortunately currently some buildfarm animals don't like the test for
> reasons I don't quite understand. Looks like it's all windows + msys
> animals that run the tap tests.  On jacana and fairywren the new test
> fails, but with a somewhat confusing problem:
>
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=jacana&dt=2020-10-01%2015%3A32%3A34
> Bail out!  aborting wait: program timed out
> # stream contents: >>data
> # (0 rows)
> # <<
> # pattern searched for: (?m-xis:^\\(0 rows\\)$)
>
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=fairywren&dt=2020-10-01%2014%3A12%3A13
> Bail out!  aborting wait: program timed out
> stream contents: >>data
> (0 rows)
> <<
> pattern searched for: (?^m:^\\(0 rows\\)$)
>
> I don't know with the -xis indicates on jacana, and why it's not present
> on fairywren. Nor do I know why the pattern doesn't match in the first
> place, sure looks like it should?
>
> Andrew, do you have an insight into how mingw's regex match differs
> from native windows and proper unixoid systems? I guess it's somewhere
> around line endings or such?
>
> Jacana successfully deals with 013_crash_restart.pl, which does use the
> same mechanis as the new 021_row_visibility.pl - I think the only real
> difference is that I used ^ and $ in the regexes in the latter...


My strong suspicion is that we're getting unwanted CRs. Note the
presence of numerous instances of this in PostgresNode.pm:

    $stdout =~ s/\r\n/\n/g if $Config{osname} eq 'msys';

So you probably want something along those lines at the top of the loop
in send_query_and_wait:

    $$psql{stdout} =~ s/\r\n/\n/g if $Config{osname} eq 'msys';

possibly also for stderr, just to make it more futureproof, and at the
top of the file:

    use Config;


Do you want me to test that first?


The difference between the canonical way perl states the regex is due to
perl version differences. It shouldn't matter.


cheers


andrew


-- 
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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