| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Maciek Sakrejda <msakrejda(at)truviso(dot)com> |
| Cc: | Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: SORT performance - slow? |
| Date: | 2011-05-23 17:27:13 |
| Message-ID: | BANLkTi=GYb1adpUyoGSJVKj13dmEw9wz1g@mail.gmail.com |
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| Lists: | pgsql-performance |
On Mon, May 23, 2011 at 1:01 PM, Maciek Sakrejda <msakrejda(at)truviso(dot)com> wrote:
>> You're probably reading it wrong. The sort itself takes about 1 ms (just
>> subtract the numbers in "actual=").
>
> I thought it was cost=startup_cost..total_cost. That is not quite the
> same thing, since startup_cost is effectively "cost to produce first
> row", and Sort can't really operate in a "streaming" fashion (well,
> theoretically, something like selection sort could, but that's beside
> the point) so it needs to do all the work up front. I'm no explain
> expert, so someone please correct me if I'm wrong.
You are right.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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