Re: Performance question 83 GB Table 150 million rows, distinct select - Mailing list pgsql-performance

On Wed, Nov 16, 2011 at 4:59 PM, Tomas Vondra <tv@fuzzy.cz> 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%.