Horton

RE: Slow catchup of 2PC (twophase) transactions on replica in LR

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

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From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
To: 'Amit Kapila' <amit.kapila16@gmail.com>, Ajin Cherian <itsajin@gmail.com>
Cc: Давыдов Виталий <v.davydov@postgrespro.ru>, Heikki Linnakangas <hlinnaka@iki.fi>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2024-04-11T02:07:33Z
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. Fix random failure in 021_twophase.

  2. Allow altering of two_phase option of a SUBSCRIPTION.

  3. Doc: use true|false rather than on|off for "failover" option

  4. Support an optional asynchronous commit mode, in which we don't flush WAL

Dear Amit,

> One naive idea is that on the publisher we can remember whether the
> prepare has been sent and if so then only send commit_prepared,
> otherwise send the entire transaction. On the subscriber-side, we
> somehow, need to ensure before applying the first change whether the
> corresponding transaction is already prepared and if so then skip the
> changes and just perform the commit prepared. One drawback of this
> approach is that after restart, the prepare flag wouldn't be saved in
> the memory and we end up sending the entire transaction again. One way
> to avoid this overhead is that the publisher before sending the entire
> transaction checks with subscriber whether it has a prepared
> transaction corresponding to the current commit. I understand that
> this is not a good idea even if it works but I don't have any better
> ideas. What do you think?

Alternative idea is that worker pass a list of prepared transaction as new
option in START_REPLICATION. This can reduce the number of inter-node
communications, but sometimes the list may be huge.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/