Re: Query much faster with enable_seqscan=0

Greg Smith <greg@2ndquadrant.com> writes:
> and the query optimizer needs to be careful about what it does and
> doesn't pull from disk.  If that's not the case, like here where there's
> 8GB of RAM and a 7GB database, dramatic reductions to both seq_page_cost
> and random_page_cost can make sense.  Don't be afraid to think lowering
> below 1.0 is going too far--something more like 0.01 for sequential and
> 0.02 for random may actually reflect reality here.

If you are tuning for an all-in-RAM situation, you should set
random_page_cost equal to seq_page_cost (and usually set both smaller
than 1).  By definition, those costs are equal if you're fetching from
RAM.  If it's only mostly-in-RAM then keeping random_page_cost a bit
higher makes sense.

            regards, tom lane