Re: Improve "select count(*)" query - takes more than 30 mins for some large tables

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От Raj kumar
Тема Re: Improve "select count(*)" query - takes more than 30 mins for some large tables
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Msg-id CACxU--VB9_7ou_C0AJ7f2acKN7XvrHsabnCRx4fdo=i5ukVWHA@mail.gmail.com
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Ответ на Re: Improve "select count(*)" query - takes more than 30 mins for some large tables  (Florents Tselai <florents.tselai@gmail.com>)
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Thanks Florents,

I tried psql -c "select count(*)" . It has brought down the time from 30 minutes to 2 minutes.
Thanks alot.

Thanks  Holger,
I'm going to try this query now.

Thanks,
Raj Kumar

On Mon, Jul 11, 2022 at 12:53 PM Florents Tselai <florents.tselai@gmail.com> wrote:


> On 11 Jul 2022, at 10:16 AM, Raj kumar <rajkumar820999@gmail.com> wrote:
>
> Hi,
>
> 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’ve had slow count(*) or count (distinct id), eventually
I’ve resorted to Unix tools.

psql “select id from my_table" | sort -u | wc -l   

The convenience/performance tradeoff depends heavily on your schema.
After all unix streams don’t know much about your integrity requirements.

>
> Thanks,
> Raj

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