Query related to Logical Replication using test_decoding and unchanged-toast-datum

From: Kiran K V <kirankv(dot)1982(at)gmail(dot)com>
To: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Query related to Logical Replication using test_decoding and unchanged-toast-datum
Date: 2025-01-06 14:19:47
Message-ID: CAGv0ivrBc=X6iaWA9Fng7u8D5BbM6EbcNy-4xF0DGFrAV+c2zw@mail.gmail.com
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Hi,

I am currently using PostgreSQL version 16 and the test_decoding plugin to
perform logical replication (using replication slots). I have a simple
table with integer column and JSON column. When a non-JSON column is
updated, the value "unchanged-toast-datum" for the JSON column is obtained.
This shows that the value recorded in a TOAST table for a JSON column value
has not changed and is as expected. could you please tell me whether
PostgreSQL will truly log these values to WAL or not ? If not, what will be
entered into WAL for the JSON column if it remains unchanged?

Please let me know. Thank you very much.

Regards,
Kiran

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