Re: Get table total page quantity and cached page quantity - Mailing list pgsql-hackers

From otar shavadze
Subject Re: Get table total page quantity and cached page quantity
Date
Msg-id CAG-jOyArZisbXcn1TPcx=1UR=RLGOEfWvPqxV_4EhzVSYFnT5g@mail.gmail.com
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In response to Re: Get table total page quantity and cached page quantity  (David Rowley <dgrowleyml@gmail.com>)
List pgsql-hackers
Answer is pretty clear, thank you David.

On Mon, Aug 16, 2021 at 12:31 AM David Rowley <dgrowleyml@gmail.com> wrote:
On Sun, 15 Aug 2021 at 23:41, otar shavadze <oshavadze@gmail.com> wrote:
> SELECT
> (SELECT relpages FROM pg_class where oid = 'public.my_table'::regclass::oid ) AS table_pages_quantity_total,
> (SELECT COUNT(DISTINCT relblocknumber) FROM pg_buffercache WHERE relfilenode = (
> SELECT relfilenode FROM pg_class WHERE oid = 'public.my_table'::regclass::oid -- (SELECT rel_oid FROM my_cte)
> ) ) AS table_pages_quantity_in_cache;
>
>  This shows that table have only one page, while second column shows 3 unique pages in buffer cache. Seems I'm measuring those numbers incorrectly(?) can you please help, which column is incorrect (or may be both) ?

This question likely is more suited to the pgsql-general mailing list.
My answer in [1] likely will clear this up for you.

If you need further information, please ask on that thread.

David

[1] https://www.postgresql.org/message-id/CAApHDvpHddfoZOviYXiz2dCr9emrrbnJ7n3HkS8KNsD9W1wscA@mail.gmail.com

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