Re: Kernel cache vs shared_buffers

[Heikki Linnakangas <heikki(at)enterprisedb(dot)com>]

Michael van Rooyen wrote:
> I have no idea regarding the inner working of the pg's shared cache, but 
> what I would like to find out is whether it is table-row-based, or 
> disk-block-based.  

It's block based.

> In the case of it being disk-block based, my 
> inclination would be to let the kernel do the buffering.  In the case of 
> the cache being table-row-based, I would expect it to be much more 
> space-efficient and I would be inclined to give the memory to the pg.  
> In that case, is it feasible to set shared_buffers to something like 
> 500000 x 8k blocks?  We make extensive use of indexes on the larger 
> tables and would seldom, if ever, do sequential scans.

A common rule of thumb people quote here is to set shared_buffers to 1/4 
of available RAM, and leave the rest for OS cache. That's probably a 
good configuration to start with.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com