Re: limit order by performance issue

2012/10/15 Pedro Jiménez <p(dot)jimenez(at)ismsolar(dot)com>:
> Hello,
> I'm trying to do a simple SQL query over Postgresl 9.0 running on Ubuntu.
>
> I have a large table (over 100 million records) with three fields, id_signal
> (bigint), time_stamp (timestamp) and var_value (float).
>
> My query looks like this:
>
> select var_value from ism_floatvalues where id_signal = 29660 order by
> time_stamp desc limit 1;
>
> So I want to select the last value from a determinated ID (is_signal).
>
> This query runs FOREVER, while if I delete "limit 1" it runs instantly....

did you ANALYZE your tables?

Can you send EXPLAIN ANALYZE result of both queries?

Regards

Pavel Stehule

>
> Any help?
>
> Regards.
>
>
>
>
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