Tom Lane wrote:
> ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp> writes:
>> Our documentation says
>> | analyze threshold = analyze base threshold
>> | + analyze scale factor * number of tuples
>> | is compared to the total number of tuples inserted, updated, or deleted
>> | since the last ANALYZE.
>
>> but deleted tuples are not considered in the total number, because the delta
>> of {n_live_tuples + n_dead_tuples} is not changed by DELETE. We add the number
>> of DELETE into n_live_tuples and subtract it from n_dead_tuples.
>
> Yeah, I was concerned about that when I was making the patch, but didn't
> see any simple fix. A large number of DELETEs (without any inserts or
> updates) would trigger a VACUUM but not an ANALYZE, which in the worst
> case would be bad because the stats could have shifted.
>
> We could fix this at the cost of carrying another per-table counter in
> the stats info, but I'm not sure it's worth it.
I believe that whenever autovacuum performs a VACUUM it actually
performs a VACUUM ANALYZE at leas the old contrib version did and I
think Alvaro copied that.