Re: about explain analyze

From: Teodor Sigaev <teodor(at)sigaev(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: about explain analyze
Date: 2003-11-28 20:07:43
Message-ID: 3FC7AB0F.8080503@sigaev.ru
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Tom, I am afraid that I don't understand. My first example:
wow=# explain analyze select max(click.accesses) from click;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------
Aggregate (cost=1103.70..1103.70 rows=1 width=8) (actual
time=289.391..289.393 rows=1 loops=1)
-> Seq Scan on click (cost=0.00..971.36 rows=52936 width=8) (actual
time=0.013..133.943 rows=52936 loops=1)
Total runtime: 289.498 ms
(3 rows)

Time: 290,695 ms

select max() returns only one row... If you mean rows in Seq Scan than
gettimeofday was called (52936+1)*2. Huge value :(

Tom Lane wrote:
> Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
>
>>How many times is gettimeofday called?
>
>
> Twice per plan node visit, if you are doing EXPLAIN ANALYZE. (The
> number of "visits" is one more than the number of rows returned.)
>
> regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru

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