| From: | Florents Tselai <florents(dot)tselai(at)gmail(dot)com> |
|---|---|
| To: | Raj kumar <rajkumar820999(at)gmail(dot)com> |
| Cc: | Pgsql-admin <pgsql-admin(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Improve "select count(*)" query - takes more than 30 mins for some large tables |
| Date: | 2022-07-11 07:23:01 |
| Message-ID: | 1B1927BA-F7DE-40E8-8F67-BCC001CD4C6B@gmail.com |
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| Thread: | |
| Lists: | pgsql-admin |
> On 11 Jul 2022, at 10:16 AM, Raj kumar <rajkumar820999(at)gmail(dot)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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