Re: [HACKERS] mat views stats

On 2/22/17 06:31, Jim Mlodgenski wrote:
> Matviews already show up in the pg_stat_*_tables and the patch does
> leverage the existing pg_stat_*_tables underlying structure, but it
> creates more meaningful pg_stat_*_matviews leaving out things like
> insert and update counts.  

But fields like seq_scans and last_analyze are then redundant between
the *_tables view and the *_matviews view.  Maybe it would make more
sense to introduce a new view like you propose and not show them in
*_tables anymore?

> I was originally thinking 2 patches, but I couldn't think of a way to
> trigger the analyze reliably without adding a refresh count or sending
> bogus stats. We can certainly send a stats message containing the number
> of rows inserted by the refresh, but are we going to also send the
> number of deletes as well? Consider a matview that has month to date
> data. At the end of the month, there will be about 30n live tuples. The
> next day on the new month, there will be n inserts with the stats
> thinking there are 30n live tuples which is below the analyze scale
> factor.  We want to analyze the matview on the first of the day of the
> new month, but it wouldn't be triggered for a few days. We can have
> REFRESH also track live tuples, but it was quickly becoming a slippery
> slope of changing behavior for a back patch. Maybe that's OK and we can
> go down that road.

For those not reading the patch, it introduces a new reloption
autovacuum_analyze_refresh_threshold that determines when to autoanalyze
a materialized view.

What behavior would we like by default?  Refreshing a materialized view
is a pretty expensive operation, so I think scheduling an analyze quite
aggressively right afterwards is often what you want.

I think sending a stats message with the number of inserted rows could
make sense.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services