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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Wed, 7 Dec 2022 08:14:32 +0530
Message-ID: 
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Subject: Re: Force streaming every change in logical decoding
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, Dec 6, 2022 at 7:18 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Tue, Dec 6, 2022 at 7:29 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Tue, Dec 6, 2022 at 11:53 AM shiy.fnst@fujitsu.com
> > <shiy.fnst@fujitsu.com> wrote:
> > >
> > > Hi hackers,
> > >
> > > In logical decoding, when logical_decoding_work_mem is exceeded, the changes are
> > > sent to output plugin in streaming mode. But there is a restriction that the
> > > minimum value of logical_decoding_work_mem is 64kB. I tried to add a GUC to
> > > allow sending every change to output plugin without waiting until
> > > logical_decoding_work_mem is exceeded.
> > >
> > > This helps to test streaming mode. For example, to test "Avoid streaming the
> > > transaction which are skipped" [1], it needs many XLOG_XACT_INVALIDATIONS
> > > messages. With the new option, it can be tested with fewer changes and in less
> > > time. Also, this new option helps to test more scenarios for "Perform streaming
> > > logical transactions by background workers" [2].
> > >
> >
> > Yeah, I think this can also help in reducing the time for various
> > tests in test_decoding/stream and
> > src/test/subscription/t/*_stream_*.pl file by reducing the number of
> > changes required to invoke streaming mode.
>
> +1
>
> > Can we think of making this
> > GUC extendible to even test more options on server-side (publisher)
> > and client-side (subscriber) cases? For example, we can have something
> > like logical_replication_mode with the following valid values: (a)
> > server_serialize: this will serialize each change to file on
> > publishers and then on commit restore and send all changes; (b)
> > server_stream: this will stream each change as currently proposed in
> > your patch. Then if we want to extend it for subscriber-side testing
> > then we can introduce new options like client_serialize for the case
> > being discussed in the email [1].
>
> Setting logical_replication_mode = 'client_serialize' implies that the
> publisher behaves as server_stream? or do you mean we can set like
> logical_replication_mode = 'server_stream, client_serialize'?
>

The latter one (logical_replication_mode = 'server_stream,
client_serialize'). The idea is to cover more options with one GUC and
each option can be used individually as well as in combination with
others.

-- 
With Regards,
Amit Kapila.