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From: [email protected] <[email protected]>
To: 'vignesh C' <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: RE: Handle infinite recursion in logical replication setup
Date: Tue, 1 Mar 2022 10:42:27 +0000
Message-ID: <TYAPR01MB5866C758B1185217950ED13CF5029@TYAPR01MB5866.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <CALDaNm0gwjY_4HFxvvty01BOT01q_fJLKQ3pWP9=9orqubhjcQ@mail.gmail.com>
References: <CALDaNm0gwjY_4HFxvvty01BOT01q_fJLKQ3pWP9=9orqubhjcQ@mail.gmail.com>

Hi Vignesh,

> In logical replication, currently Walsender sends the data that is
> generated locally and the data that are replicated from other
> instances. This results in infinite recursion in circular logical
> replication setup.

Thank you for good explanation. I understand that this fix can be used
for a bidirectional replication.

> Here there are two problems for the user: a) incremental
> synchronization of table sending both local data and replicated data
> by walsender b) Table synchronization of table using copy command
> sending both local data and replicated data

So you wanted to solve these two problem and currently focused on
the first one, right? We can check one by one.

> For the first problem "Incremental synchronization of table by
> Walsender" can be solved by:
> Currently the locally generated data does not have replication origin
> associated and the data that has originated from another instance will
> have a replication origin associated. We could use this information to
> differentiate locally generated data and replicated data and send only
> the locally generated data. This "only_local" could be provided as an
> option while subscription is created:
> ex: CREATE SUBSCRIPTION sub1 CONNECTION 'dbname =postgres port=5433'
> PUBLICATION pub1 with (only_local = on);

Sounds good, but I cannot distinguish whether the assumption will keep.

I played with your patch, but it could not be applied to current master.
I tested from bd74c40 and I confirmed infinite loop was not appeared.

local_only could not be set from ALTER SUBSCRIPTION command.
Is it expected?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED

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