Re: Simple Query Very Slow

On 2012-12-22 13:06:21 +0100, Alban Hertroys wrote:
> > and here's my query
> >
> > select * from ticket
> > where created between '2012-12-19 00:00:00' and '2012-12-20 00:00:00'
> >
> > This was working fine until the number of records started to grow (about 5 million) and now it's taking forever to return.
> >
> > Explain analyze reveals this:
> >
> > "Index Scan using ticket_1_idx on ticket (cost=0.00..10202.64 rows=52543 width=1297) (actual time=0.109..125.704 rows=53340 loops=1)"
> > " Index Cond: ((created >= '2012-12-19 00:00:00+00'::timestamp with time zone) AND (created <= '2012-12-20 00:00:00+00'::timestamp with time zone))"
> > "Total runtime: 175.853 ms"
>
> > Nothing works. What am I doing wrong? why is it selecting sequential scan? the indexes are supposed to make the query fast. Anything that can be done to optimize it?

Whats the time you would need? Beause the above isn't that slow. Perhaps
the timing youre seing from your application includes transferring the
data over a not too fast link?

It would be interesting to see EXPLAIN (ANALYZE, BUFFERS) $query

> It is not selecting sequential scan, you're looking at an index scan. That should be pretty fast, and it isn't that slow - that's still sub-second performance (0.176s).
> Is that explain from the correct table? According to the results there are but 53 thousand rows in it, not anywhere near 5 million.

Well, thats the estimate *after* applying the restriction, so that seems
sensible.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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