On 2013-04-05 00:38, Merlin Moncure wrote:
On Thu, Apr 4, 2013 at 4:32 PM, Condor <condor@xxxxxxxxxx> wrote:
Hello,
I have one query in my postgresql 9.2.3 that took 137 ms to me
executed and
looking a way
what I can do to optimize it. I have one table generated numbers from
1 to 1
000 000 and
I need to get first free id, meanwhile id's when is taken can be free
(deleted data and id
is free for next job). Table is simple:
id serial,
jobid text,
valids int default 0
(Yes, I have index).
my query is: SELECT jobid FROM mytable WHERE valids = 0 ORDER BY id
ASC
LIMIT 1
I need the first id only.
My question is: Is there a way how I can avoid using ORDER BY to
receive the
first
free id from mytable ?
well, you can (via EXISTS()), but you can really optimize this with
partial index.
CREATE INDEX ON mytable (id) WHERE valids = 0;
then,
SELECT jobid FROM mytable WHERE valids = 0 ORDER BY id ASC LIMIT 1;
should return in zero time since btree indexes can optimize order by
expressions and the partial index will bypass having to wade through
the rows you don't want.
merlin
Hm,
I only can say: Thank You!
Your solution is work, but Im now a little confused. I has a index
CREATE INDEX ON mytable (valids) USING BTREE (valids) and the
query to find valids = 0 tooks 137 ms.
Why, your solution is worked ? Yes, it's worked.
Cheers,
Condor
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