Re: VACUUM ANALYZE suddenly taking forever

Try running pgstattuple on some of the tables that have not had vacuum full,
and some of those that have. It will tell you how many dead tuples there are
in the table, which is an indicator of how seriously the table needs a full
vacuum.

Run IPCS on the Unix command line to see how much of your SHMMAX is being
used? You may have reached a threshold in one of the 6 Postgres parameters
that use SHMMAX causing a slowdown, like max_fsm_pages (see the report at
the end of a database vacuum full output).

On 7/28/06, Nolan Cafferky <Nolan(dot)Cafferky(at)rbsinteractive(dot)com> wrote:
>
> Synopsis: VACUUM ANALYZE on full database used to take just a few
> minutes, now it takes several hours, with no apparant improvement in
> successive runs.
>
> Details:
>
> I have a production database server hosting two heavily used databases
> and not much else. We're currently running postgres 8.0.8. Normally we
> have a VACUUM ANALYZE run nightly on both databases, which only takes a
> couple of minutes each to complete. We also have a report that runs
> hourly on one of the databases and dumps a large amount of data into a
> materialized view. It normally takes 10-20 minutes (we could probably
> optimize it, but it's never made it up the priority list).
>
> Anyway, about two nights ago, the hourly report started running
> indefinitely, and we've had to turn it off, after having 16 copies of it
> waiting in line for the first to finish. Since then, VACUUM ANALYZE has
> been taking several hours instead of several minutes on both databases.
> Yesterday I ran the VACUUM ANALYZE manually on both databases, hoping
> that there was just some transient cleanup problem, but we've had the
> same results today.
>
> What would cause this, and what can I do to fix it? For the moment, I'm
> going to claim the "we didn't change anything!" mantra - no development
> we've done in the past few days seems like it would significantly
> influence both databases. The so far untried ideas I've had are:
>
> * Try out the autovacuum service
> * Re-index tables (this hasn't been done for at least months, maybe never)
> * Do some selective VACUUM FULL on high-use tables (materialized view
> for report seems like a likely culprit, but also seems like it wouldn't
> influence both databases)
> * Restart postgres, restart the machine itself, and other useless
> handwaving
>
> \begin{more-background-information}
>
> * The database server is a quad Opteron, about 2GHz each. 8 GB of RAM,
> and a several hard disk RAID. It's burly. I believe we're running on a
> Gentoo linux installation, although postgres was installed from source.
> Again, we're running postgres 8.0.8. Here's some sample output from a
> "vmstat 1 5" that I just ran:
> procs -----------memory---------- ---swap-- -----io---- --system--
> ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy
> id wa
> 0 0 1208 5658464 0 2256384 0 0 554 344 1 1 10
> 2 83 6
> 1 0 1208 5640272 0 2273928 0 0 24 476 1405 1885 12
> 3 83 2
> 1 0 1208 5652368 0 2258628 0 0 0 560 1194 663 6
> 1 91 2
> 0 0 1208 5653392 0 2259104 0 0 16 750 1979 4362 15
> 4 78 2
> 1 0 1208 5649744 0 2259716 0 0 24 661 1651 3114 21
> 4 73 2
> * Yes, so far we've been doing a direct VACUUM ANALYZE on everything,
> plus VACUUM FULL ANALYZE on a few tables, instead of using the
> autovacuum service like we should. It seems like there wouldn't be such
> an abrupt change in performace because of that.
> * Shortly after killing the 16 or so backed-up reports, the partition
> postgres had the data/subtrans directory in filled up, and we had a
> bunch of "No space left on device" errors for a minute or two. The
> partitions do deserve some rearranging, but for now we've made some
> adjustments and postgres is wallowing in free disk space.
>
> \end{more-background-information}
>
> Suggestions?
>
> --
> Nolan Cafferky
> Software Developer
> IT Department
> RBS Interactive
> nolan(dot)cafferky(at)rbsinteractive(dot)com
>
>
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