Re: AW: [HACKERS] create index updates nrows statistics

>
> > > a create index updates the statistics in pg_class,
> > > this leads to substantial performance degradation compared to
> > > 6.4.2.
> >
> > Create index did that in 6.4.2 as well --- how could it be making
> > performance worse?
> >
> I am not sure why, but in 6.4.2 a create table, create index, insert,
> select * from tab where indexedcol=5 did actually use the index path,
> even if table reltuples and relpages was 0.
> It currently uses a seq scan, which is exactly what we wanted to avoid
> in the newly created table case, but do want on an actually small table.
>
> Please apply the patch I previously sent.

From memory not verified:

Doesn't CREATE INDEX update pg_statistics? I think it does so
the faked statistics only cause different joins to happen as
long as there is no index created immediately after CREATE
TABLE (HASHJOIN vs. NESTLOOP).

Jan

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