Horton

Re: 040_pg_createsubscriber.pl is slow and unstable (was Re: speed up a logical replica setup)

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, Noah Misch <noah@leadboat.com>, Alexander Lakhin <exclusion@gmail.com>, Euler Taveira <euler@eulerto.com>, Amit Kapila <amit.kapila16@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Michael Paquier <michael@paquier.xyz>, Andres Freund <andres@anarazel.de>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Fabrízio de Royes Mello <fabriziomello@gmail.com>, vignesh C <vignesh21@gmail.com>
Date: 2024-07-29T20:18:32Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pg_createsubscriber: Remove obsolete comment

  2. pg_createsubscriber: Fix an unpredictable recovery wait time.

  3. Fix unstable test in 040_pg_createsubscriber.

  4. Fix the testcase introduced in commit 81d20fbf7a.

  5. Further weaken new pg_createsubscriber test on Windows.

  6. Temporarily(?) weaken new pg_createsubscriber test on Windows.

  7. Make pg_createsubscriber warn if publisher has two-phase commit enabled.

  8. Make pg_createsubscriber more wary about quoting connection parameters.

  9. pg_createsubscriber: Remove failover replication slots on subscriber

  10. pg_createsubscriber: Remove replication slot check on primary

  11. pg_createsubscriber: Only --recovery-timeout controls the end of recovery process

  12. pg_createsubscriber: creates a new logical replica from a standby server

  13. Add some const decorations

  14. Add option force_initdb to PostgreSQL::Test::Cluster:init()

  15. Remove MSVC scripts

Robert Haas <robertmhaas@gmail.com> writes:
> On Sun, Jun 30, 2024 at 2:40 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> ... However, I added a new open item about how the
>> 040_pg_createsubscriber.pl test is slow and still unstable.

> But that said, I see no commits in the commit history which purport to
> improve performance, so I guess the performance is probably still not
> what you want, though I am not clear on the details.

My concern is described at [1]:

>> I have a different but possibly-related complaint: why is
>> 040_pg_createsubscriber.pl so miserably slow?  On my machine it
>> runs for a bit over 19 seconds, which seems completely out of line
>> (for comparison, 010_pg_basebackup.pl takes 6 seconds, and the
>> other test scripts in this directory take much less).  It looks
>> like most of the blame falls on this step:
>> 
>> [12:47:22.292](14.534s) ok 28 - run pg_createsubscriber on node S
>> 
>> AFAICS the amount of data being replicated is completely trivial,
>> so that it doesn't make any sense for this to take so long --- and
>> if it does, that suggests that this tool will be impossibly slow
>> for production use.  But I suspect there is a logic flaw causing
>> this.  Speculating wildly, perhaps that is related to the failure
>> Alexander spotted?

The followup discussion in that thread made it sound like there's
some fairly fundamental deficiency in how wait_for_end_recovery()
detects end-of-recovery.  I'm not too conversant with the details
though, and it's possible that pg_createsubscriber is just falling
foul of a pre-existing infelicity.

If the problem can be correctly described as "pg_createsubscriber
takes 10 seconds or so to detect end-of-stream", then it's probably
only an annoyance for testing and not something that would be fatal
in the real world.  I'm not quite sure if that's accurate, though.

			regards, tom lane

[1] https://www.postgresql.org/message-id/flat/2377319.1719766794%40sss.pgh.pa.us#bba9f5ee0efc73151cc521a6bd5182ed