Re: [HACKERS] Wrong index choosen?

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Matthew T. O'Connor wrote:

| Gaetano Mendola wrote:
|
|> Tom Lane wrote:
|> | Given the nature of the data (login times), I'd imagine that the
|> problem
|> | is simply that he hasn't analyzed recently enough.  A bump in stats
|> | target may not be needed, but he's going to have to re-analyze that
|> | column often if he wants this sort of query to be estimated accurately,
|> | because the fraction of entries later than a given time T is *always*
|> | going to be changing.
|>
|> Well know that I think about it, I felt my shoulders covered by
|> pg_autovacuum but looking at the log I see that table never analyzed!
|> Aaargh.
|>
|> I already applied the patch for the autovacuum but evidently I have to
|> make it more aggressive, I'm sorry that I can not made him more
|> aggressive
|> only for this table.
|
|
| Yeah, the version of autovacuum in 7.4 contrib doesn't allow table
| specific settings.  The patch I have sumbitted for 7.5 does, so
| hopefully this will be better in the future.
|
| You can however set the VACUUM and ANALYZE thresholds independently. So
| perhpaps it will help you if you set your ANALYZE setting to be very
| aggressive and your VACUUM settings to something more standard.

Well I think pg_autovacuum as is in 7.4 can not help me for this particular
table.

The table have 4.8 milions rows and I have for that table almost 10252 new
entries for day.

I'm using pg_autovacuum with -a 200 -A 0.8 this means a threashold for
that table equal to:  3849008 and if I understod well the way pg_autovacuum
works this means have an analyze each 375 days, and I need an analyze for
each day, at least.

So I think is better for me put an analyze for that table in the cron.

Am I wrong ?


Regards
Gaetano Mendola



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