Re: [COMMITTERS] pgsql: Add pages deleted from pending list to FSM

On Fri, Sep 18, 2015 at 6:27 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> [ moving thread to -hackers ]
>
> Fujii Masao <masao(dot)fujii(at)gmail(dot)com> writes:
> > So autoanalyze still doesn't call IndexFreeSpaceMapVacuum().
> > That is, only backend can clean the list in INSERT-only workload.
> > I don't think that this is desirable. Because the backend will
> > periodically take a big performance penalty.
>

Calling IndexFreeSpaceMapVacuum is only need to reuse the space freed up by
cleaning the pending list.

The list is still getting cleaned and truncated by autoanalyze, it is just
that the space is not getting marked for reuse.

When I wrote this, my thought was that a table vacuum is going to call
IndexFreeSpaceMapVacuum() from another place in its code and so should not
call it here as well. I neglected to consider the autoanalyze case.

> > So I'm thinking that even autoanalyze should call
> IndexFreeSpaceMapVacuum()
> > to clean the list in a background, in order to avoid such spikes in
> > INSERT response time. Thought?
>

But it already is cleaning the list. If that space is not marked as
reusable, that causes index bloat, but doesn't cause latency spikes.

> It seems quite bizarre for auto-analyze to do that. auto-vacuum, sure,
> but I do not think this should get plugged into ANALYZE.
>

It may be odd that autoanalyze cleans the list at all (which this patch
doesn't change), but given that it does clean the list I don't see why it
would be bizarre to make the cleaned-up space re-usable.

Cheers,

Jeff