[
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: 10.4.0.0
> Environment: OS: All
> JVM: All
> Reporter: Ole Solberg
> Priority: Minor
>
> SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS() on
> '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
> '
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
