Re: explain analyze reports that my queries are fast but they run very slowly

Nikolas Everett <nik9000(at)gmail(dot)com> writes:
> On Thu, Dec 27, 2012 at 4:33 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Nikolas Everett <nik9000(at)gmail(dot)com> writes:
>>> We straced the backend during the explain and it looked like the open
>>> commands were taking several seconds each.

>> Kind of makes me wonder if you have a whole lot of tables ("whole lot"
>> in this context probably means tens of thousands) and are storing the
>> database on a filesystem that doesn't scale well to lots of files in one
>> directory. If that's the explanation, the reason the 8.3 installation
>> was okay was likely that it was stored on a more modern filesystem.

> We have 1897 files for our largest database which really isn't a whole lot.

OK...

> The old servers were EXT3 over FC to a NetApp running RHEL5 PPC. The new
> servers are on NFS to the same NetApp running RHEL5 Intel.

Now I'm wondering about network glitches or NFS configuration problems.
This is a bit outside my expertise unfortunately, but it seems clear
that your performance issue is somewhere in that area.

regards, tom lane