Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1

On 9/10/07, Gregory Stark <stark(at)enterprisedb(dot)com> wrote:
>
> "Luke Lonergan" <llonergan(at)greenplum(dot)com> writes:
>
> > Should be a lot higher, something like 10-15 is approximating accurate.
>
> Most people's experience is that due to Postgres underestimating the benefits
> of caching lowering the random_page_cost is helpful.

Quite often the real problem is that they have effective_cache_size
too small, and they use random_page_cost to get the planner to switch
to index scans on small tables. With a large effective_cache_size and
small to moderate table (i.e. it fits in memory pretty handily) the
planner seems much better in the last few major releases about picking
an index over a sequential scan.