Re: Deceiding which index to use

Mezei Zoltán wrote:
> Richard Huxton wrote:
>>
>> OK - so the next place to look is the distribution of values for
>> subscriber_id on the output_message_log. Does that have some subscribers
>> with many rows and lots with hardly any?
>>
> Hmm... There are about 1.5k subscribers with 100-200 messages each - all the
> other 19k has an average of 8.9 messages, most of them having only 1 message. I
> think that's exactly the situation you mention...

[snip alter table ... set statistics]

> So if I'm correct: this statistics gathering can be fine tuned, and if i set the
> <num> to 1000 then not only the first 10 subsribers (with most messages) will be
> stored in pg_stats, but the first 1000? Is 1000 a hard-coded
> highest-possible-value? I think it would be best to set that to simething like
> 1800-1900 as I have about that many subscibers with high message count.

There is a cost to increasing the stats values, otherwise it'd already
be set at 1000. In your case I'm not sure if 100-200 vs 8-9 messages is
enough to skew things. Only one way to find out...

--
Richard Huxton
Archonet Ltd