Horton

Re: logical decoding and replication of sequences, take 2

Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>

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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Date: 2023-07-28T12:44:45Z
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. Migrate logical slots to the new node during an upgrade.

  2. Make test_decoding ddl.out shorter

  3. Fix snapshot handling in logicalmsg_decode

  4. doc: Adjust a few more references to "postmaster"

  5. Revert "Logical decoding of sequences"

On Wed, Jul 26, 2023 at 8:48 PM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
>
> Anyway, I was thinking about this a bit more, and it seems it's not as
> difficult to use the page LSN to ensure sequences don't go backwards.
> The 0005 change does that, by:
>
> 1) adding pg_sequence_state, that returns both the sequence state and
>    the page LSN
>
> 2) copy_sequence returns the page LSN
>
> 3) tablesync then sets this LSN as origin_startpos (which for tables is
>    just the LSN of the replication slot)
>
> AFAICS this makes it work - we start decoding at the page LSN, so that
> we  skip the increments that could lead to the sequence going backwards.
>

I like this design very much. It makes things simpler than complex.
Thanks for doing this.

I am wondering whether we could reuse pg_sequence_last_value() instead
of adding a new function. But the name of the function doesn't leave
much space for expanding its functionality. So we are good with a new
one. Probably some code deduplication.

-- 
Best Wishes,
Ashutosh Bapat