On Oct 22, 2013 1:14 AM, "Tomas Vondra" <tv@fuzzy.cz> wrote:
>
> On 22.10.2013 00:59, sparikh wrote:
> > Yes, Expalin without Analyze is taking long. It is weird. In the
> > pg_stat_activity Explain was the only query running. So server was
> > almost idle. Using New relic interface I checked CPU was almost idle
> > - around 10-20%. There were some IO activity - around 40-50%.
> >
> > I forgot to mention before I could run perf on command line even with
> > root permission. It says command not found. May be utility is not
> > installed or not enabled.
>
> Obviously you need to install it ... maybe ask your sysadmin to do that.
>
> > I have attached the snapshot of vmstat while explain was running in
> > background. vmstat.txt
> > <http://postgresql.1045698.n5.nabble.com/file/n5775349/vmstat.txt>
>
> The vmstat clearly shows that ~1 CPU is waiting on I/O. Hmm, I'm really
> wondering what's going on here - I can't think of a case where this
> would happen with a plain EXPLAIN ...
Catalog bloat could make that happen. Though that should show up on the master as well, it could be that it's cached there and therefor only shows us to as cpu and not io and is therefore not noticed.
/Magnus
