On 08/12/2011 04:24 PM, Vick Khera wrote:
> 2011/8/10 Ondrej Ivanič<ondrej.ivanic@gmail.com>:
>
>> Ups! Well spotted Tomas! The actual values are:
>> random_page_cost = 2
>> seq_page_cost = 1
>>
>>
> With the SSD I would set these to the same value of 1. That's what I do.
>
That probably makes sense on your RAMSAN. Sequential access on FusionIO
drives is at least 3X as fast as completely random though, and
worst-case it can be even slower relative to what a sequential scan can
deliver. It's not the >50X difference seen on regular drives, but
there's an easily measurable gap. I'm not sure if it's that the flash
cells deliver stuff faster when you read a sequential series from the
same cell of flash, or if it's just that there's less physical IOs
happening.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
