Re: Performance question 83 GB Table 150 million rows, distinct select

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Tomas Vondra <tv(at)fuzzy(dot)cz>
Cc: Tory M Blue <tmblue(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Performance question 83 GB Table 150 million rows, distinct select
Date: 2011-11-17 01:57:54
Message-ID: CAOR=d=2ZHAf=jubZXXOFOHyrwGqf-UUGwZ6TO0sHjbTzDN6_-Q@mail.gmail.com
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On Wed, Nov 16, 2011 at 4:59 PM, Tomas Vondra <tv(at)fuzzy(dot)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%.

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