On 17 Listopad 2011, 2:57, Scott Marlowe wrote: > On Wed, Nov 16, 2011 at 4:59 PM, Tomas Vondra <tv@xxxxxxxx> wrote: > >> But you're right - you're not bound by I/O (although I don't know what >> are >> those 15% - iowait, util or what?). The COUNT(DISTINCT) has to actually >> keep all the distinct values to determine which are actually distinct. > > Actually I meant to comment on this, he is IO bound. Look at % Util, > it's at 99 or 100. > > Also, if you have 16 cores and look at something like vmstat you'll > see 6% wait state. That 6% represents one CPU core waiting for IO, > the other cores will add up the rest to 100%. Aaaah, I keep forgetting about this and I somehow ignored the iostat results too. Yes, he's obviously IO bound. But this actually means the pre-aggregating the data (as I described in my previous post) would probably help him even more (less data, less CPU). Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
