Re: Slow updates, poor IO

Hi Greg,

I've got 32M shared on a 1G machine and 16 checkpoint segments.
I'll run some tests against 64 segments and see what happens.

Your previous postings were extremely helpful wrt the MVCC issue.
I thank you!

-john


Greg Smith wrote:
> On Fri, 26 Sep 2008, John Huttley wrote:
>
>> running    update file set perms='0664' took about 10 mins
>
> What do you have checkpoint_segments and shared_buffers set to?  If
> you want something that's doing lots of updates to perform well, you
> need to let PostgreSQL have a decent size chunk of memory to buffer
> the index writes with, so it's more likely they'll get combined into
> larger and therefore more easily sorted blocks rather than as more
> random ones.  The randomness of the writes is why your write rate is
> so slow.  You also need to cut down on the frequency of checkpoints
> which are very costly on this type of statement.
>
> Also:  which version of PostgreSQL?  8.3 includes an improvement aimed
> at updates like this you might benefit from.
>
> --
> * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
>