Re: 2nd Level Buffer Cache

On 3/21/11 3:24 AM, Greg Stark wrote:
>> 2-level caches work well for a variety of applications.
> 
> I think 2-level caches with simple heuristics like "pin all the
> indexes" is unlikely to be helpful. At least it won't optimize the
> average case and I think that's been proven. It might be helpful for
> optimizing the worst-case which would reduce the standard deviation.
> Perhaps we're at the point now where that matters.

You're missing my point ... Postgres already *has* a 2-level cache:
shared_buffers and the FS cache.  Anything we add to that will be adding
levels.

We already did that, actually, when we implemented ARC: effectively gave
PostgreSQL a 3-level cache.  The results were not very good, although
the algorithm could be at fault there.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com