Horton

Re: snapbuild woes

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Petr Jelinek <petr.jelinek@2ndquadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>, Erik Rijkers <er@xs4all.nl>, Robert Haas <robertmhaas@gmail.com>, Craig Ringer <craig@2ndquadrant.com>
Date: 2017-04-24T22:59:57Z
Lists: pgsql-hackers

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Hi,

On 2017-04-15 05:18:49 +0200, Petr Jelinek wrote:
> Hi, here is updated patch (details inline).

I'm not yet all that happy, sorry:

Looking at 0001:
- GetOldestSafeDecodingTransactionId() only guarantees to return an xid
  safe for decoding (note how procArray->replication_slot_catalog_xmin
  is checked), not one for the initial snapshot - so afaics this whole
  exercise doesn't guarantee much so far.
- A later commit introduces need_full_snapshot as a
  CreateInitDecodingContext, but you don't use it, not here.  That seems
  wrong.
- I remain unhappy with the handling of the reset of effective_xmin in
  FreeDecodingContext(). What if we ERROR/FATAL out before that happens?

What do you think about something like the attached?  I've not yet
tested it any way except running the regression tests.

- Andres

Commits

  1. Fix thinko introduced in 2bef06d516460 et al.

  2. Avoid superfluous work for commits during logical slot creation.

  3. Fix race condition leading to hanging logical slot creation.

  4. Don't use on-disk snapshots for exported logical decoding snapshot.

  5. Preserve required !catalog tuples while computing initial decoding snapshot.