Re: Logical Replication of sequences

Amit Kapila <amit.kapila16@gmail.com>

From: Amit Kapila <amit.kapila16@gmail.com>

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

Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Peter Eisentraut <peter@eisentraut.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Euler Taveira <euler@eulerto.com>, Michael Paquier <michael@paquier.xyz>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Hou, Zhijie/侯志杰 <houzj.fnst@fujitsu.com>, Sawada Masahiko <sawada.mshk@gmail.com>, "Katz, Jonathan" <jkatz@amazon.com>

Date: 2024-06-06T03:52:26Z

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 →

Doc: Add documentation for sequence synchronization.
- 55cefadde874 19 (unreleased) landed
Remove unused assignment in CREATE PUBLICATION grammar.
- bfb7419b0bbe 19 (unreleased) landed
Add seq_sync_error_count to subscription statistics.
- f6a4c498dcf6 19 (unreleased) landed
Fix few issues in commit 5509055d69.
- 5a4eba558aa7 19 (unreleased) landed
Add sequence synchronization for logical replication.
- 5509055d6956 19 (unreleased) landed
Add worker type argument to logical replication worker functions.
- 3e8e05596a02 19 (unreleased) landed
Introduce "REFRESH SEQUENCES" for subscriptions.
- f0b3573c3aac 19 (unreleased) landed
Refactor logical worker synchronization code into a separate file.
- 41c674d2e31e 19 (unreleased) landed
Standardize use of REFRESH PUBLICATION in code and messages.
- 2436b8c047ff 19 (unreleased) landed
Add "ALL SEQUENCES" support to publications.
- 96b378497346 19 (unreleased) landed
Expose sequence page LSN via pg_get_sequence_data.
- b93172ca59f4 19 (unreleased) landed
Resume conflict-relevant data retention automatically.
- 0d48d393d465 19 (unreleased) cited
Post-commit review fixes for 228c370868.
- 1f7e9ba3ac4e 19 (unreleased) cited
Generate GUC tables from .dat file
- 63599896545c 19 (unreleased) cited

On Wed, Jun 5, 2024 at 6:01 PM Ashutosh Bapat
<ashutosh.bapat.oss@gmail.com> wrote:
>
> On Wed, Jun 5, 2024 at 8:45 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>>
>>  How about periodically sending this information?
>> >
>>
>> Now, if we want to support some sort of failover then probably this
>> will help. Do you have that use case in mind?
>
>
> Regular failover was a goal for supporting logical replication of sequences. That might be more common than major upgrade scenario.
>

We can't support regular failovers to subscribers unless we can
replicate/copy slots because the existing nodes connected to the
current publisher/primary would expect that. It should be primarily
useful for major version upgrades at this stage.

>>
>> If we want to send
>> periodically then we can do it when decoding checkpoint
>> (XLOG_CHECKPOINT_ONLINE) or some other periodic WAL record like
>> running_xacts (XLOG_RUNNING_XACTS).
>>
>
> Yeah. I am thinking along those lines.
>
> It must be noted, however, that none of those optional make sure that the replicated sequence's states are consistent with the replicated object state which use those sequences.
>

Right, I feel as others are advocating, it seems better to support it
manually via command and then later we can extend it to do at shutdown
or at some regular intervals. If we do that then we should be able to
support major version upgrades and planned switchover.

-- 
With Regards,
Amit Kapila.