Hi,
I notices a weird thing here.
version 7.2.1
on Solaris
table "test", has a field "state".
There are 4 "state" values, 1, 2, 3, 4.
select count(*) from test group by state;
took 11500 msec
but
select count(*) from test where state = 1;
select count(*) from test where state = 2;
select count(*) from test where state = 3;
select count(*) from test where state = 4;
total took 626 msec
Why ??
thanks,
kathy
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TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html 3 2195
When was the last time you vacuumed full?
Kathy Zhu wrote: Hi,
I notices a weird thing here.
version 7.2.1 on Solaris
table "test", has a field "state". There are 4 "state" values, 1, 2, 3, 4.
select count(*) from test group by state; took 11500 msec
but
select count(*) from test where state = 1; select count(*) from test where state = 2; select count(*) from test where state = 3; select count(*) from test where state = 4; total took 626 msec
Why ??
thanks, kathy ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ?
http://www.postgresql.org/docs/faqs/FAQ.html
---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster
On Fri, 3 Oct 2003, Kathy Zhu wrote: Hi,
I notices a weird thing here.
version 7.2.1 on Solaris
table "test", has a field "state". There are 4 "state" values, 1, 2, 3, 4.
select count(*) from test group by state; took 11500 msec
but
select count(*) from test where state = 1; select count(*) from test where state = 2; select count(*) from test where state = 3; select count(*) from test where state = 4; total took 626 msec
Why ??
First thought was caching: the disk blocks are cached in memory after the first
qery so all the others just fetch from there.
Second thought: well I haven't really had it but indexes and sorting is sort of
sloshing around in my mind. Not sure how that applies to here since I can't
remember if the first would require the sort step having retrieved all the
tuples and the others would just use the index pages.
It is Friday though.
--
Nigel J. Andrews
---------------------------(end of broadcast)---------------------------
TIP 8: explain analyze is your friend
On Fri, 3 Oct 2003, Kathy Zhu wrote: Hi,
I notices a weird thing here.
version 7.2.1 on Solaris
table "test", has a field "state". There are 4 "state" values, 1, 2, 3, 4.
select count(*) from test group by state; took 11500 msec
but
select count(*) from test where state = 1; select count(*) from test where state = 2; select count(*) from test where state = 3; select count(*) from test where state = 4; total took 626 msec
I believe Solaris's qsort implementation (which is used for the group by)
has problems dealing with large numbers of similar values.
I think in later versions of pg our own qsort is used.
Kris Jurka
---------------------------(end of broadcast)---------------------------
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