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From "A B (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2916) Change/error? in 'Ordered null semantics' output from 'SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS()' in lang/wisconsin.java
Date Mon, 30 Jul 2007 15:53:52 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12516426

A B commented on DERBY-2916:

Thank you for taking the time to investigate this issue, Bryan.

I am not very familiar with the particular peformance optimization that is described here,
but your explanation seems reasonable to me based on what I could grasp from the code comments
(the code comments themselves are a tad hard to follow).

> Unfortunately, I'm not quite sure whether the change in output means that the optimizer
is now 
> including the performance optimization for column 0, and was not including it before,
or vice versa.

The code comments suggest that the intended optimization is to "treat [the index column] as
though nulls are ordered".  So given that we know are seeing "null ordered semantics" on column
"0" where we were not before, I think this is a case where we now include a performance optimization
that we didn't include before.  If that's the correct conclusion then Dan's change is enabling
an optimization that didn't exist before, in which case I think it is a good thing.  So the
resolution to this issue would simply be to update the master...(and maybe the make the associated
code comments a bit clearer, if possible...)

Thanks again for your input, Bryan!

> Change/error? in 'Ordered null semantics' output from 'SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS()'
in lang/wisconsin.java
> -----------------------------------------------------------------------------------------------------------------------
>                 Key: DERBY-2916
>                 URL: https://issues.apache.org/jira/browse/DERBY-2916
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions:
>         Environment: OS: All
> JVM: All
>            Reporter: Ole Solberg
>            Priority: Minor
> 'Statement Text: 
> 	select * from TENKTUP1
> 		left outer join TENKTUP2 on
> 		(
> 			TENKTUP1.unique1 = TENKTUP2.unique1
> 		)
> 		left outer join ONEKTUP on
> 		(
> 			TENKTUP2.unique2 = ONEKTUP.unique2
> 		)
> 		left outer join BPRIME on
> 		(
> 			ONEKTUP.onePercent = BPRIME.onePercent
> 		)
> '
> now returns extra "0" in
> '	Ordered null semantics on the following columns: 
> 0 
> 					stop position: 
> 	> on first 1 column(s).
> 	Ordered null semantics on the following columns: 
> 0 
> '

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