Re: Speed up Clog Access by increasing CLOG buffers

Hi,

On 2015-09-07 10:34:10 -0300, Alvaro Herrera wrote:
> I wonder if it would make sense to explore an idea that has been floated
> for years now -- to have pg_clog pages be allocated as part of shared
> buffers rather than have their own separate pool. That way, no separate
> hardcoded allocation limit is needed. It's probably pretty tricky to
> implement, though :-(

I still think that'd be a good plan, especially as it'd also let us use
a lot of related infrastructure. I doubt we could just use the standard
cache replacement mechanism though - it's not particularly efficient
either... I also have my doubts that a hash table lookup at every clog
lookup is going to be ok performancewise.

The biggest problem will probably be that the buffer manager is pretty
directly tied to relations and breaking up that bond won't be all that
easy. My guess is that the best bet here is that the easiest way to at
least explore this is to define pg_clog/... as their own tablespaces
(akin to pg_global) and treat the files therein as plain relations.

Greetings,

Andres Freund