RE: [HACKERS] Caution: tonight's commits force initdb

> -----Original Message-----
> From: owner-pgsql-hackers(at)postgreSQL(dot)org
> [mailto:owner-pgsql-hackers(at)postgreSQL(dot)org]On Behalf Of Zeugswetter
> Andreas IZ5
> Sent: Tuesday, August 24, 1999 6:48 PM
> To: pgsql-hackers
> Subject: AW: [HACKERS] Caution: tonight's commits force initdb
>
>
>
> > Hmm,Index scan is chosen to select all rows.
> > AFAIK,sequential scan + sort is much faster than index scan in
> > most cases.
> >
> > cost of index scan < cost of sequential scan + cost of sort
> >
> This is usually true. It might need resources though that are not
> available,

Without taking SORT into account

[From my example]

cost of sequential scan = 1716.32 and
cost of index scan = 2284.55

cost of sequential scan > cost of index scan * 0.7

It's unbelievable for me.

> e.g. 8 GB sort space. It also depends on whether the application is
> interested in
> first row (interactive), or all row performance (batch). Other DB's can
> switch modes
> to decide on the wanted behavior. So I think there is no yes/no
> decision on
> this.
>

We could use LIMIT clause to get first rows now and optimizer
should take LIMIT/OFFSET into account(TODO item).

Regards.

Hiroshi Inoue
Inoue(at)tpf(dot)co(dot)jp