Horton

Re: Why only some files have fsm and vm extensions

Laurenz Albe <laurenz.albe@cybertec.at>

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From: Laurenz Albe <laurenz.albe@cybertec.at>
To: "Subramanian,Ramachandran" <ramachandran.subramanian@alte-leipziger.de>, "pgsql-novice@lists.postgresql.org" <pgsql-novice@lists.postgresql.org>
Date: 2026-05-20T12:51:19Z
Lists: pgsql-novice 
On Wed, 2026-05-20 at 09:48 +0000, Subramanian,Ramachandran wrote:
> I am beginning to read the internals of Postgres , got curious and looked at the actual files .
> I learnt that FSM contains the Space map and vm the visibility map for a given table.
>  
>    1. Why only some tables have it and others do not?

The ones that don't have these files have never been processed by VACUUM.

>    2. Why for some tables fsm is bigger than the table itself?

Because the tables are very small.

Yours,
Laurenz Albe