Horton

Re: AW: Trying to understand Tuple Header

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>, "David G. Johnston" <david.g.johnston@gmail.com>
Cc: "pgsql-novice@lists.postgresql.org" <pgsql-novice@lists.postgresql.org>
Date: 2026-05-04T07:32:52Z
Lists: pgsql-novice 
On Mon, 2026-05-04 at 04:04 +0000, Subramanian,Ramachandran wrote:
> So the next select to the table cross references the pg_xact file to check if hint bits
> need to be updated or not ?  How deep does the next select look into the pg_xact file ?
> For example if I roll back and never touch this table for 30  Minutes and I come back
> and do a second select…will it look back into 30 mins of history in pg_xact ?

Yes.  It has to, to maintain correctness.

If nobody ever looks at the row, eventually autovacuum will freeze it.  Any pg_xact
segment that only contains transactions older than the oldest unfrozen row will
get reclaimed.

Yours,
Laurenz Albe