Horton

Re: logical decoding and replication of sequences, take 2

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Dilip Kumar <dilipbalaut@gmail.com>
Date: 2023-12-06T13:50:45Z
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 12/6/23 11:19, Amit Kapila wrote:
> On Sun, Dec 3, 2023 at 11:56 PM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
>>
>> On 12/3/23 18:52, Tomas Vondra wrote:
>>> ...
>>>
>>
>> Another idea is that maybe we could somehow inform ReorderBuffer whether
>> the output plugin even is interested in sequences. That'd help with
>> cases where we don't even want/need to replicate sequences, e.g. because
>> the publication does not specify (publish=sequence).
>>
>> What happens now in that case is we call ReorderBufferQueueSequence(),
>> it does the whole dance with starting/aborting the transaction, calls
>> rb->sequence() which just does "meh" and doesn't do anything. Maybe we
>> could just short-circuit this by asking the output plugin somehow.
>>
>> In an extreme case the plugin may not even specify the sequence
>> callbacks, and we're still doing all of this.
>>
> 
> We could explore this but I guess it won't solve the problem we are
> facing in cases where all sequences are published and plugin has
> specified the sequence callbacks. I think it would add some overhead
> of this check in positive cases where we decide to anyway do send the
> changes.

Well, the idea is the check would be very simple (essentially just a
boolean flag somewhere), so not really measurable.

And if the plugin requests decoding sequences, I guess it's natural it
may have a bit of overhead. It needs to do more things, after all. It
needs to be acceptable, ofc.

regards

-- 
Tomas Vondra
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