Re: More vacuum stats

On Mon, Aug 23, 2010 at 16:38, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Magnus Hagander <magnus(at)hagander(dot)net> writes:
>> On Mon, Aug 23, 2010 at 16:28, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
>>> What I actually want here is for the time that the last table autovacuum
>>> started, adding to the finish time currently exposed by pg_stat_user_tables.
>
>> Now, that would be quite useful. That'd require another stats message,
>> since we don't send anything on autovacuum start, but I don't think
>> the overhead of that is anything we need to worry about - in
>> comparison to an actual vacuum...
>
> No, you wouldn't really need an extra message, you could just send both
> start and finish times in the completion message.  I'm not sure that
> having last start time update before last end time would be a good idea
> anyway.

Hmm, good point. We'd just need an extra field in that message.

> But in any case it's true that an extra message wouldn't be a
> significant cost.  What I'd be more concerned about is the stats table
> bloat from adding yet another per-table field.  That could be a lot of
> space on an installation with lots of tables.
>
>> We could also store last_autovacuum_vacuum_duration - is that better
>> or worse than start and end time?
>
> No, I think you want to know the actual time not only the duration.

Well, you could calculate one from the other - especially if one takes
less size, per your comment above.

--
 Magnus Hagander
 Me: http://www.hagander.net/
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