Re: pg_prewarm

On Wed, Jun 20, 2012 at 3:53 PM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> I'm worried about the overlap with pgfincore.  It's pretty well
> established in this space, and has about 73% feature overlap with
> pg_prewarm, while having more features all together.  So it would seem
> to me that it would be better to add whatever is missing to pgfincore
> instead.  Or split pgfincore, as suggested above, but that would upset
> existing users.  But adding severely overlapping stuff for no technical
> reasons (or there any?) doesn't sound like a good idea.

73%? I think it's got about 15% overlap.

The biggest problem with pgfincore from my point of view is that it
only works under Linux, whereas I use a MacOS X machine for my
development, and there is also Windows to think about. Even if that
were fixed, though, I feel we ought to have something in the core
distribution. This patch got more +1s than 95% of what gets proposed
on hackers.

> Also, Robert has accurately described this as "mechanism, not policy".
> That's fine, that's what all of our stuff is.  Replication and most of
> postgresql.conf suffers from that.  Eventually someone will want to
> create a way to save and restore various caches across server restarts,
> as discussed before.  Would that mean there will be a third way to do
> all this, or could we at least align things a bit so that such a
> facility could use most of the proposed prewarming stuff?  (Patches for
> the cache restoring exist, so it should be possible to predict this a
> little bit.)

Well, pg_buffercache + pg_prewarm is enough to save and restore shared
buffers. Not the OS cache, but we don't have portable code to query
the OS cache yet anyway.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company