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/