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Logical replication in PostgreSQL Amount of subscriber vs publisher WALs 2+ messages / 1 participants [nested] [flat]
* Logical replication in PostgreSQL Amount of subscriber vs publisher WALs @ 2026-03-24 14:06 PALAYRET Jacques <[email protected]> 0 siblings, 1 reply; 2+ messages in thread From: PALAYRET Jacques @ 2026-03-24 14:06 UTC (permalink / raw) To: [email protected] 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 ^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Logical replication in PostgreSQL Amount of subscriber vs publisher WALs Vacuuming @ 2026-03-25 16:15 PALAYRET Jacques <[email protected]> parent: PALAYRET Jacques <[email protected]> 0 siblings, 0 replies; 2+ messages in thread From: PALAYRET Jacques @ 2026-03-25 16:15 UTC (permalink / raw) To: [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 ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2026-03-25 16:15 UTC | newest] Thread overview: 2+ messages (download: mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2026-03-24 14:06 Logical replication in PostgreSQL Amount of subscriber vs publisher WALs PALAYRET Jacques <[email protected]> 2026-03-25 16:15 ` Re: Logical replication in PostgreSQL Amount of subscriber vs publisher WALs Vacuuming PALAYRET Jacques <[email protected]>
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