Re: Fix pg_buffercache document

On Thu, May 7, 2020 at 2:53 PM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> On Thu, 7 May 2020 at 18:12, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Thu, May 7, 2020 at 2:23 PM Masahiko Sawada
> > <masahiko(dot)sawada(at)2ndquadrant(dot)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."?
>
> Thank you for your idea. Agreed.
>
> Attached the updated version patch.
>

LGTM. I will commit this tomorrow unless there are more comments.

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