public inbox for [email protected]  

help / color / mirror / Atom feed

From: David Rowley <[email protected]>
To: Matthew Planchard <[email protected]>
Cc: [email protected]
Subject: Re: Dealing with SeqScans when Time-based Partitions Cut Over
Date: Fri, 19 Dec 2025 09:20:30 +1300
Message-ID: <CAApHDvpH1-GfwvAEKGb1WniOFK-f66E_Ex9fD-AqotDaq=OyXQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Fri, 19 Dec 2025 at 07:48, Matthew Planchard <[email protected]> wrote:
> * Because the planner's latest knowledge of the partition was based on
>   its state prior to the cutover, it assumes the partition is empty and
>   creates plans that use sequential scans

If the table/partition was just created and not analyzed, the planner
shouldn't consider it empty. By default, an empty table is assumed to
have 10 pages. (Check what pg_class.relpages is set to. -1 means it's
not been analyzed, 0 would mean analyzed/vacuumed when empty)

create table a (a int primary key, b int not null);
create index on a(b);
explain select * from a where a = 1;

 Index Scan using a_pkey on a  (cost=0.15..8.17 rows=1 width=8)
   Index Cond: (a = 1)

explain select * from a where b = 1;

 Bitmap Heap Scan on a  (cost=4.24..14.91 rows=11 width=8)
   Recheck Cond: (b = 1)
   ->  Bitmap Index Scan on a_b_idx  (cost=0.00..4.24 rows=11 width=0)
         Index Cond: (b = 1)

Perhaps pg_partman thinks running an ANALYZE or VACUUM on the new
partitions is a good idea? Otherwise, if you're not doing this
yourself, I don't know why you're getting a Seq Scan. It might help if
you showed the problem query and schema.

David

view thread (4+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected]
  Subject: Re: Dealing with SeqScans when Time-based Partitions Cut Over
  In-Reply-To: <CAApHDvpH1-GfwvAEKGb1WniOFK-f66E_Ex9fD-AqotDaq=OyXQ@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox