Re: Moving pgstat.stat and pgstat.tmp

On Wednesday 05 December 2007 07:22, Alvaro Herrera wrote:
> Robert Treat wrote:
> > On Monday 03 December 2007 20:22, Erik Jones wrote:
> > > Interesting. If this is anything you'd like to look into I can
> > > provide whatever diagnostic output you need (iostat, vmstat, dtrace
> > > script outputs, etc...) but I do have to reiterate that we are an
> > > extreme corner case due to out schema size. For now, is renaming the
> > > #define'd paths for the stats file and temp file sufficient for
> > > moving them? Basically, we'd like to move them onto a RAM disk to
> > > give our disks a break.
> >
> > Yeah, we've noticed the same problem (pgstat is the most active file on
> > the system... uncovered in much the same way... go solaris). Actually I
> > was wondering if it could be done with symlinks, a la moving xlogs.
>
> Not really, because a new file is created and renamed in place each time
> it's going to be rewritten. So the symlink would be lost in the first
> file rewrite.
>

Ah yeah, thats what I concluded back then.

> The first idea that comes to mind is to make the path configurable via
> GUC, so the user could set it to be written to an in-memory filesystem
> (/tmp in Solaris?).

Yep, thought of that to, though it was after feature freeze so I didn't
propose it. Course if someone wants to sneak that in it would be cool :-)

> But then I thought, why do we need it to be a file
> at all? Why not use a mmap'ed memory area or something like that, and
> only write it to a file on postmaster shutdown? (Losing the file on
> unclean shutdown is not a problem, because the file is removed anyway.)

I suppose you need some facility to spill to disk, so maybe being in a file is
better? Seems it might not be in most cases... I wonder how big a memory
space we (or Erik) need.

--
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL