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From: PALAYRET Jacques <[email protected]>
To: [email protected]
Subject: Re: Logical replication in PostgreSQL Amount of subscriber vs publisher WALs Vacuuming
Date: Wed, 25 Mar 2026 16:15:20 +0000 (GMT)
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Hello, 

Vacuuming seems to explain these differences. 
Especially for large tables, vacuuming can generate many WAL. 

Regards 

De: "PALAYRET Jacques" <[email protected]> 
À: [email protected] 
Envoyé: Mardi 24 Mars 2026 15:06:23 
Objet: Logical replication in PostgreSQL Amount of subscriber vs publisher WALs 

Hello, 

The amount of WAL generated by an SQL INSERT or UPDATE statement applied to a table with multiple indexes can be much greater than the size of the table (table + index). 
For example, an INSERT statement in an empty table (with 3 indexes) can generate WALs twice the size of the table (table + index). 
This difference (even for an INSERT) may seem surprising, but it's understandable. 

What's less intuitive is that, according to my tests, with logical replication in PostgreSQL, the amount of WAL generated by an SQL statement can be very different between the subscriber server (the replica) and the publisher server (the provider). 
Is this accurate? Sometimes 1.5 or 2 times greater? 

Regards 
----- Météo-France ----- 
PALAYRET Jacques 
DCSC/GDC 
[email protected] 
Fixe : +33 561078319 

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