Re: Unhappy about API changes in the no-fsm-for-small-rels patch - Mailing list pgsql-hackers

From Amit Kapila
Subject Re: Unhappy about API changes in the no-fsm-for-small-rels patch
Date
Msg-id CAA4eK1LiX4u13U7P6k7H-sXP1_pi0fj4VHRG2CFZMJtR7Nfvmw@mail.gmail.com
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In response to Re: Unhappy about API changes in the no-fsm-for-small-rels patch  (Alvaro Herrera <alvherre@2ndquadrant.com>)
List pgsql-hackers
On Thu, May 2, 2019 at 3:42 AM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>
> On 2019-May-01, Amit Kapila wrote:
>
> > On Tue, Apr 30, 2019 at 7:52 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>
> > > Hmm ... so, if vacuum runs and frees up any space from any of the pages,
> > > then it should send out an invalidation -- it doesn't matter what the
> > > FSM had, just that there is more free space now.  That means every other
> > > process will need to determine a fresh FSM,
> >
> > I think you intend to say the local space map because once FSM is
> > created we will send invalidation and we won't further build relcache
> > entry having local space map.
>
> Yeah, I mean the map that records free space.
>
> > > but that seems correct.  Sounds better than keeping outdated entries
> > > indicating no-space-available.
> >
> > Agreed, but as mentioned in one of the above emails, I am also bit
> > scared that it should not lead to many invalidation messages for small
> > relations, so may be we should send the invalidation message only when
> > the entire page is empty.
>
> I don't think that's a concern, is it?  You typically won't be running
> multiple vacuums per second, or even multiple vacuums per minute.
>

That's right.  So let's try by adding invalidation call whenever space
is reduced.  Is there a good way to test whether the new invalidation
calls added by this patch has any significant impact?

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



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