Re: estimating # of distinct values - Mailing list pgsql-hackers

From Tom Lane
Subject Re: estimating # of distinct values
Date
Msg-id 15389.1293760924@sss.pgh.pa.us
Whole thread Raw
In response to Re: estimating # of distinct values  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: estimating # of distinct values  (Alvaro Herrera <alvherre@commandprompt.com>)
Re: estimating # of distinct values  (Csaba Nagy <ncslists@googlemail.com>)
List pgsql-hackers
Alvaro Herrera <alvherre@commandprompt.com> writes:
> I was thinking that we could have two different ANALYZE modes, one
> "full" and one "incremental"; autovacuum could be modified to use one or
> the other depending on how many changes there are (of course, the user
> could request one or the other, too; not sure what should be the default
> behavior).

How is an incremental ANALYZE going to work at all?  It has no way to
find out the recent changes in the table, for *either* inserts or
deletes.  Unless you want to seqscan the whole table looking for tuples
with xmin later than something-or-other ... which more or less defeats
the purpose.
        regards, tom lane


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