Content-Type: text/plain;
	charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.100.31\))
Subject: Re: Improve "select count(*)" query - takes more than 30 mins for
 some large tables
From: Florents Tselai <florents.tselai@gmail.com>
In-Reply-To: 
 <CACxU--UJY4sD2SjW8V3W0oAPuuTzE3fAvBzTaej-BmUUNJxN_Q@mail.gmail.com>
Date: Mon, 11 Jul 2022 10:23:01 +0300
Cc: Pgsql-admin <pgsql-admin@lists.postgresql.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <1B1927BA-F7DE-40E8-8F67-BCC001CD4C6B@gmail.com>
References: 
 <CACxU--UJY4sD2SjW8V3W0oAPuuTzE3fAvBzTaej-BmUUNJxN_Q@mail.gmail.com>
To: Raj kumar <rajkumar820999@gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/1B1927BA-F7DE-40E8-8F67-BCC001CD4C6B%40gmail.com>
Precedence: bulk


> On 11 Jul 2022, at 10:16 AM, Raj kumar <rajkumar820999@gmail.com> =
wrote:
>=20
> Hi,
>=20
> How can I improve "select count(*)" for larger tables? I'm doing a db =
migration and need to validate the data count.
> "select count(*) " queries are taking more than 30 minutes for some =
tables which is more than the downtime we have.
> Will work_mem increase help? or how can i speed up this row count?

Personally, whenever I=E2=80=99ve had slow count(*) or count (distinct =
id), eventually=20
I=E2=80=99ve resorted to Unix tools.

psql =E2=80=9Cselect id from my_table" | sort -u | wc -l  =20

The convenience/performance tradeoff depends heavily on your schema.
After all unix streams don=E2=80=99t know much about your integrity =
requirements.

>=20
> Thanks,
> Raj