Re: How is random_page_cost=4 ok?

Gregory Stark schrieb:

> But with your numbers things look even weirder. With a 90MB/s sequential speed
> (91us) and 9ms seek latency that would be a random_page_cost of nearly 100!

Looks good :). If you actually want to base something on Real World 
numbers I'd suggest that we collect them beforehand from existing 
setups. I was introduced to IOmeter [1] at an HP performance course 
which is a nice GUI Tool which allows you to define workloads to your 
likings and test it against given block devices, unfortunately it's 
Windows only. fio [2] and Iozone [3] should do the same for the 
Unix-World, without the "nice" and "GUI" parts ;).


For improving the model - in what situations would we benefit from a 
more accurate model here?


Is it correct that this is only relevant for large (if not huge) tables 
which border on (or don't fit in) effective_cache_size (and respectively 
- the OS Page cache)?

And we need the cost to decide between a sequential, index (order by, 
small expected result set) and a bitmap index scan?


Speaking of bitmap index/heap scans - are those counted against seq or 
random_page_cost?


regards,
michael

[1] http://www.iometer.org/
[2] http://freshmeat.net/projects/fio/
[3] http://www.iozone.org/