On Mon, Dec 8, 2014 at 03:40:43PM -0600, Merlin Moncure wrote:
> >> Did not see consistent measurable gains > 256
> >> effective_io_concurrency. Interesting that at setting of '2' (the
> >> lowest possible setting with the feature actually working) is
> >> pessimal.
> >
> > Very interesting. When we added a per-tablespace random_page_cost,
> > there was a suggestion that we might want to add per-tablespace
> > effective_io_concurrency someday:
>
> What I'd really like to see is to have effective_io_concurrency work
> on other types of scans. It's clearly a barn burner on fast storage
> and perhaps the default should be something other than '1'. Spinning
> storage is clearly dead and ssd seem to really benefit from the posix
> readhead api.
Well, the real question is knowing which blocks to request before
actually needing them. With a bitmap scan, that is easy --- I am
unclear how to do it for other scans. We already have kernel read-ahead
for sequential scans, and any index scan that hits multiple rows will
probably already be using a bitmap heap scan.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +