Re: Tracking last scan time

On Wed, Aug 24, 2022 at 04:01:21PM +0100, Dave Page wrote:
> On Wed, 24 Aug 2022 at 15:18, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> On Tue, Aug 23, 2022 at 10:55:09AM +0100, Dave Page wrote:
> > Often it is beneficial to review one's schema with a view to removing
> indexes
> > (and sometimes tables) that are no longer required. It's very difficult
> to
> > understand when that is the case by looking at the number of scans of a
> > relation as, for example, an index may be used infrequently but may be
> critical
> > in those times when it is used.
> >
> > The attached patch against HEAD adds optional tracking of the last scan
> time
> > for relations. It updates pg_stat_*_tables with new last_seq_scan and
> > last_idx_scan columns, and pg_stat_*_indexes with a last_idx_scan column
> to
> > help with this.
>
> Would it be simpler to allow the sequential and index scan columns to be
> cleared so you can look later to see if it is non-zero?  Should we allow
>
> I don't think so, because then stat values wouldn't necessarily correlate with
> each other, and you wouldn't know when any of them were last reset unless we
> started tracking each individual reset. At least now you can see when they were
> all reset, and you know they were reset at the same time.

Yeah, true. I was more asking if these two columns are in some way
special or if people would want a more general solution, and if so, is
that something we want in core Postgres.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

Indecision is a decision. Inaction is an action. Mark Batterson