Re: Clearing global statistics

Rafael Martinez wrote:
> One thing I miss from the statistics you can get via pg_stat_* is
> information about how long we have been collecting stats (or in other
> words, when was the last time the stats were reset)
>

I've considered adding this for the same reasons you're asking about it,
but am not happy with the trade-offs involved. The problem is that you
have to presume the server was running the entirety of the time since
stats were reset for that data to be useful. So unless people are in
that situation, they're going to get data that may not represent what
they think it does. Realistically, if you want a timestamp that always
means something useful you have to rest the stats at every server start,
which leads us to:

> Before 8.3, we had the stats_reset_on_server_start parameter and the
> pg_postmaster_start_time() function. This was an easy way of resetting
> *all* statistics delivered by pg_stat_* and knowing when this was done.
> We were able to produce stats with information about sec/hours/days
> average values in an easy way.
>

With this new feature I'm submitting, you can adjust your database
startup scripts to make this happen again. Start the server,
immediately loop over every database and call pg_stat_reset on them all,
and call pg_stat_reset_shared('bgwriter'). Now you've got completely
cleared stats that are within a second or two of
pg_postmaster_start_time(), should be close enough to most purposes.
Theoretically we could automate that better, but I've found it hard to
justify working on given that it's not that difficult to handle outside
of the database once the individual pieces are exposed.

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com