| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: estimating # of distinct values |
| Date: | 2010-12-31 02:02:04 |
| Message-ID: | 15389.1293760924@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)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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