Re: slow query - will CLUSTER help?

On 12/19/2013 03:24 PM, Sergey Konoplev wrote:

> 2. You are limited with IO
> I would also suggest you to upgrade your storage in this case.

I think this is the case. If I recall correctly, his setup includes a
single RAID-1 for everything, and he only has 32GB of RAM. In fact, the
WAL traffic from those inserts alone are likely saturating the write IO,
especially if it starts a checkpoint while the load is still going on. I
wouldn't want to be around for that.

Even with a fairly selective index, just the fetches necessary to
identify the rows and verify the data pages will choke a RAID-1 with
almost every query. Any table with several hundred million rows is also
too big to fit in cache if any significant portion of it is fetched on a
regular basis. The cache turnover is probably extremely high, too.

That workload is just too high for a system of that description. It
would be fine for a prototype, development, or possibly a QA system, but
if that's intended to be a production resource, it needs more memory and IO.

Also since I can't see part of this conversation and it doesn't seem
anyone else mentioned it, the WAL directory *must* be moved to a
separate set of disks for a workload of this volume. The amount of
writes here will constantly degrade read IO and further increase fetch
times.

--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com

______________________________________________

See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email