Re: Tuning Help - What did I do wrong?

On 10/4/07, Josh Trutwin <josh(at)trutwins(dot)homeip(dot)net> wrote:
> We have a pretty busy linux server running postgres 8.1.4, waiting to
> upgrade until 8.3 to avoid dump/restoring twice.

You should immediate update your version to 8.1.whateverislatest.
That requires no dump / restore and it is a bug fix update. I doubt
this problem is because you're out of date on patches, but who
knows...

> # cat /proc/meminfo
> total: used: free: shared: buffers: cached:
> Mem: 3704217600 3592069120 112148480 0 39460864 2316271616
> Swap: 2516918272 270336 2516647936

Well, you've got plenty of memory, and a large chunk is being used as cache.

> The postgresql.conf was basically the default so I decided to
> increase the cache size and a couple paramaters to make more use of
> that memory - here's what I did:
>
> shared_buffers = 16384 (was 1000)
> work_mem = 16384 (was 1024)
> wal_buffers = 24 (was 8)
> checkpoint_segments = 5 (was 3)
> effective_cache_size = 10000 (was 1000)
> stats_command_string = on (was off)
> stats_block_level = on (was off)
> stats_row_level = on (was off)

Your changes seem reasonable.

> Also, the entire cluster gets vacuumed analyzed nightly.

You should look into running the autovacuum daemon. for heavily used
databases nightly vacuuming may not be enough.

> After making these changes, the performance on the server actually
> worsened. I slowly backed off on some of the paramaters but didn't
> seem to help.

Most likely turning on stats collection slowed you down a bit.

We need to see examples of what's slow, including explain analyze
output for slow queries. Also a brief explanation of the type of load
your database server is seeing. I.e. is it a lot of little
transactions, mostly read, batch processing, lots of users, one user,
etc... Right now we don't have enough info to really help you.