Horton

RE: speed up a logical replica setup

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

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From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
To: 'Euler Taveira' <euler@eulerto.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Date: 2024-07-30T03:56:15Z
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

Dear Euler,

> Hayato already mentioned one of the solution in a previous email [2].
> AFAICS we can use any solution that creates a WAL record. I tested the
> following options:

Yes, my point was that we should add an arbitrary record after the recovery_target_lsn.

> (a) temporary replication slot: requires an additional replication slot.
> small payload. it is extremely slow in comparison with the other
> options.
> (b) logical message: can be consumed by logical replication when/if it
> is supported some day. big payload. fast.
> (c) snapshot of running txn:  small payload. fast.
> (d) named restore point: biggest payload. fast.

Another PoV is whether they trigger the flush of the generated WAL record. You've
tested pg_logical_emit_message() with flush=false, but this meant that the WAL does
not flush so that the wait_for_end_recovery() waits a time. IIUC, it may wait 15
seconds, which is the time duration bgwriter works. If flush is set to true, the
execution time will be longer.
pg_create_restore_point() also does not flush the generated record so that it may
be problematic. Moreover, the name of the restore point might be a conflict that
users will use.

Overall, I could agree to use pg_log_standby_snapshot(). This flushes the WAL
asynchronously but ensures the timing is not so delayed.

Best regards,
Hayato Kuroda
FUJITSU LIMITED