I was looking at the autovacuum documentation:
http://www.postgresql.org/docs/9.0/interactive/routine-vacuuming.html#AUTOVACUUM
For analyze, a similar condition is used: the threshold, defined as:
analyze threshold = analyze base threshold + analyze scale factor *
number of tuples
is compared to the total number of tuples inserted or updated since
the last ANALYZE.
I guess that should be updated to read "insert, updated or deleted".
On Mon, Sep 20, 2010 at 10:12 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Joe Miller <joe.d.miller@gmail.com> writes:
>> The autovacuum daemon currently uses the number of inserted and
>> updated tuples to determine if it should run VACUUM ANALYZE on a
>> table. Why doesn’t it consider deleted tuples as well?
>
> I think you misread the code.
>
> Now there *is* a problem, pre-9.0, if your update pattern is such that
> most or all updates are HOT updates. To quote from the 9.0 alpha
> release notes:
>
> Revise pgstat's tracking of tuple changes to
> improve the reliability of decisions about when to
> auto-analyze. The previous code depended on n_live_tuples +
> n_dead_tuples - last_anl_tuples, where all three of these
> numbers could be bad estimates from ANALYZE itself. Even
> worse, in the presence of a steady flow of HOT updates and
> matching HOT-tuple reclamations, auto-analyze might never
> trigger at all, even if all three numbers are exactly right,
> because n_dead_tuples could hold steady.
>
> It's not clear to me if that matches your problem, though.
>
> regards, tom lane
>
