Re: explain analyze reports that my queries are fast but they run very slowly - Mailing list pgsql-performance

From Tom Lane
Subject Re: explain analyze reports that my queries are fast but they run very slowly
Date
Msg-id 21869.1356649951@sss.pgh.pa.us
Whole thread Raw
In response to Re: explain analyze reports that my queries are fast but they run very slowly  (Nikolas Everett <nik9000@gmail.com>)
Responses Re: explain analyze reports that my queries are fast but they run very slowly  (Nikolas Everett <nik9000@gmail.com>)
List pgsql-performance
Nikolas Everett <nik9000@gmail.com> writes:
> On Thu, Dec 27, 2012 at 4:33 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Nikolas Everett <nik9000@gmail.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


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