> Selectivity is computed during index creation (fast_load).

Ahhh.. So does that explain why a gbak restore will build
selectivity and a empty database freshly populated does not?

Markus




It

> is stored as part of the index description on the index root
> page (IRT). It is also computed by BTR_selectivity which
> traverses the index leaf pages.
>
> Selectivity is referenced in exact one place in the optimizer
> to estimate the cardinality resulting from a potential partial
> join to compute least cost join order.
>
> There are cases where a more accurate selectivity will produce
> a faster join, but they are few and far between. Bad optimization
> is usually the result of bugs in the optimizer, not bad input.
>
> Please note the selectivity is never used to determine whether
> or not an index will be used.
>
> Jim Starkey
>
> ------------------------------------------------------------------------
> Accurate impartial advice on everything from laptops to table saws.
> http://click.egroups.com/1/3020/3/_/830676/_/957020941/
> ------------------------------------------------------------------------
>
> To unsubscribe from this group, send an email to:
> IB-Architect-unsubscribe@onelist.com