Re: [PERFORM] Large time difference between explain analyze and normal run

2005-02-10 Thread Tom Lane 
Chris Kratz [EMAIL PROTECTED] writes:
 Does anyone have any idea why there be over a 4s difference between running 
 the statement directly and using explain analyze?

  Aggregate  (cost=9848.12..9848.12 rows=1 width=0) (actual 
 time=4841.231..4841.235 rows=1 loops=1)
-  Seq Scan on answer  (cost=0.00..8561.29 rows=514729 width=0) (actual 
 time=0.011..2347.762 rows=530576 loops=1)
  Total runtime: 4841.412 ms

EXPLAIN ANALYZE's principal overhead is two gettimeofday() kernel calls
per plan node execution, so 1061154 such calls here.  I infer that
gettimeofday takes about 4 microseconds on your hardware ... which seems
a bit slow for modern machines.  What sort of box is it?

regards, tom lane

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Re: [PERFORM] Large time difference between explain analyze and normal run

2005-02-10 Thread Chris Kratz 
On Thursday 10 February 2005 01:58 pm, Tom Lane wrote:
 Chris Kratz [EMAIL PROTECTED] writes:
  Does anyone have any idea why there be over a 4s difference between
  running the statement directly and using explain analyze?
 
   Aggregate  (cost=9848.12..9848.12 rows=1 width=0) (actual
  time=4841.231..4841.235 rows=1 loops=1)
 -  Seq Scan on answer  (cost=0.00..8561.29 rows=514729 width=0)
  (actual time=0.011..2347.762 rows=530576 loops=1)
   Total runtime: 4841.412 ms

 EXPLAIN ANALYZE's principal overhead is two gettimeofday() kernel calls
 per plan node execution, so 1061154 such calls here.  I infer that
 gettimeofday takes about 4 microseconds on your hardware ... which seems
 a bit slow for modern machines.  What sort of box is it?

   regards, tom lane

OK, that makes sense.

Athlon XP 3000+
1.5G Mem

Is there a way to test the gettimeofday() directly?

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