Re: Understanding/reading set option show_* on

Hi Mike,

Ok, I got it.

Most information of set option show_* output are for engineering to investigate an issue.

Please set show_pio_costing on instead of show_lio_costing
and then you can find estimated join cost for each join condition.
ASE uses a cost-based optimizer and it selects the cheapest cost of them as final plan.

For example,

set rowcount 5

go

set option show_pio_costing on

go

select * from sysobjects, sysindexes where sysobjects.id=sysindexes.id

go

After running the sql, you can find some estimated join costing and the final plan selected by optimizer.

( PopNlJoin ( PopRidJoin ( PopIndScan csysindexes sysindexes ) ) ( PopRidJoin ( PopIndScan csysobjects sysobjects ) ) )

cost:243.8729 T(L10.83051,P8.830508,C14.49153) tempdb:0 order: none

( PopMergeJoin ( PopRidJoin ( PopIndScan csysindexes sysindexes ) ) ( PopRidJoin ( PopIndScan csysobjects sysobjects ) )

) cost:262.3606 T(L9.333358,P8.746773,C250.2458) O(L0,P0,C228) tempdb:0 order: none

( PopNlJoin ( PopRidJoin ( PopIndScan csysindexes sysindexes ) ) ( PopRidJoin ( PopIndScan csysobjects sysobjects ) ) )

cost:243.8729 T(L10.83051,P8.830508,C14.49153) tempdb:0 order: none

( PopMergeJoin ( PopRidJoin ( PopIndScan csysobjects sysobjects ) ) ( PopRidJoin ( PopIndScan csysindexes sysindexes ) )

) cost:286.7606 T(L9.333358,P8.746773,C494.2458) O(L0,P0,C472) tempdb:0 order: none

( PopNlJoin ( PopRidJoin ( PopIndScan csysobjects sysobjects ) ) ( PopRidJoin ( PopIndScan csysindexes sysindexes ) ) )

cost:238.9948 T(L13.9181,P8.322345,C31) tempdb:0 order: none

FINAL PLAN ( total cost = 238.9948 ):

        lio=13.9181 pio=8.322345 cpu=31 tempdb=0

ASE optimizer selected last Nested Loop Join because it was the cheapest cost.

thanks,
Jongun Seo