Re: Fix pg_buffercache document

On Thu, May 7, 2020 at 2:23 PM Masahiko Sawada
<masahiko.sawada@2ndquadrant.com> wrote:
>
> Hi,
>
> The following description in pg_buffercace is no longer true.
>
> When the pg_buffercache view is accessed, internal buffer manager
> locks are taken for long enough to copy all the buffer state data that
> the view will display. This ensures that the view produces a
> consistent set of results, while not blocking normal buffer activity
> longer than necessary. Nonetheless there could be some impact on
> database performance if this view is read often.
>
> We changed pg_buffercache_page so that it doesn't take buffer manager
> locks in commit 6e654546fb6. Therefore from version 10,
> pg_buffercache_page has less impact on normal buffer activity less but
> might not return a consistent snapshot across all buffers instead.
>

+1.

There is a typo in the patch (queris/queries).  How about if slightly
reword it as "Since buffer manager locks are not taken to copy the
buffer state data that the view will display, accessing
<structname>pg_buffercache</structname> view has less impact on normal
buffer activity but it doesn't provide a consistent set of results
across all buffers.  However, we ensure that the information of each
buffer is self-consistent."?

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com