Horton

Re: speed up a logical replica setup

Euler Taveira <euler@eulerto.com>

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From: "Euler Taveira" <euler@eulerto.com>
To: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>, "'pgsql-hackers@lists.postgresql.org'" <pgsql-hackers@lists.postgresql.org>
Cc: "Shlok Kyal" <shlok.kyal.oss@gmail.com>, "vignesh C" <vignesh21@gmail.com>, "Michael Paquier" <michael@paquier.xyz>, "Peter Eisentraut" <peter@eisentraut.org>, "Andres Freund" <andres@anarazel.de>, "Ashutosh Bapat" <ashutosh.bapat.oss@gmail.com>, "Amit Kapila" <amit.kapila16@gmail.com>
Date: 2024-01-23T23:58:11Z
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

On Mon, Jan 22, 2024, at 4:06 AM, Hayato Kuroda (Fujitsu) wrote:
> I analyzed and found a reason. This is because publications are invisible for some transactions.
> 
> As the first place, below operations were executed in this case.
> Tuples were inserted after getting consistent_lsn, but before starting the standby.
> After doing the workload, I confirmed again that the publication was created.
> 
> 1. on primary, logical replication slots were created.
> 2. on primary, another replication slot was created.
> 3. ===on primary, some tuples were inserted. ===
> 4. on standby, a server process was started
> 5. on standby, the process waited until all changes have come.
> 6. on primary, publications were created.
> 7. on standby, subscriptions were created.
> 8. on standby, a replication progress for each subscriptions was set to given LSN (got at step2).
> =====pg_subscriber finished here=====
> 9. on standby, a server process was started again
> 10. on standby, subscriptions were enabled. They referred slots created at step1.
> 11. on primary, decoding was started but ERROR was raised.

Good catch! It is a design flaw.

> In this case, tuples were inserted *before creating publication*.
> So I thought that the decoded transaction could not see the publication because
> it was committed after insertions.
> 
> One solution is to create a publication before creating a consistent slot.
> Changes which came before creating the slot were surely replicated to the standby,
> so upcoming transactions can see the object. We are planning to patch set to fix
> the issue in this approach.

I'll include a similar code in the next patch and also explain why we should
create the publication earlier. (I'm renaming
create_all_logical_replication_slots to setup_publisher and calling
create_publication from there and also adding the proposed GUC checks in it.)


--
Euler Taveira
EDB   https://www.enterprisedb.com/