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: Amit Kapila <amit.kapila16@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Noah Misch <noah@leadboat.com>, Alexander Lakhin <exclusion@gmail.com>, Euler Taveira <euler@eulerto.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: 2024-07-30T04:26:31Z
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

Amit Kapila <amit.kapila16@gmail.com> writes:
> On Tue, Jul 30, 2024 at 1:48 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> If the problem can be correctly described as "pg_createsubscriber
>> takes 10 seconds or so to detect end-of-stream",

> The problem can be defined as: "pg_createsubscriber waits for an
> additional (new) WAL record to be generated on primary before it
> considers the standby is ready for becoming a subscriber". Now, on
> busy systems, this shouldn't be a problem but for idle systems, the
> time to detect end-of-stream can't be easily defined.

Got it.  IMO, that absolutely will be a problem for real users,
not only test cases.

> One of the proposed solutions is that pg_createsubscriber generate a
> dummy WAL record on the publisher/primary by using something like
> pg_logical_emit_message(), pg_log_standby_snapshot(), etc. This will
> fix the problem (BF failures and slow detection for end-of-stream) but
> sounds more like a hack.

It's undoubtedly a hack, but I like it anyway because it's small,
self-contained, and easily removable once we have a better solution.
As you say, it seems a bit late in the v17 cycle to be designing
anything more invasive.

			regards, tom lane