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https://issues.apache.org/jira/browse/DERBY-3330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569987#action_12569987
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Anurag Shekhar commented on DERBY-3330:
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Thanks Mike for pointing out the possibility of having empty page and hence
need to scan multiple page.
I will reintroduce the code for the same. I will add code to keep moving left
(or right) till a row is found or no more leaf is available.
Locking of left or right row is attempted only if there is a duplicate is
found. In that case
a. The transaction was deleted in same transaction -- So its already locked
within same transaction
b. Is deleted in some other transaction - It will result in losing the latch
and a rescan will performed to identify the slot (no lock)
c. Is an valid row - an exception will be thrown and lock will be released
immediately.
Irrespective of the isolation level only update lock is requested. But the
actual locking is performed only in case c and that too for a very short time,
I think it won't have much impact on performance.
> provide support for unique constraint over nullable columns
> -----------------------------------------------------------
>
> Key: DERBY-3330
> URL: https://issues.apache.org/jira/browse/DERBY-3330
> Project: Derby
> Issue Type: New Feature
> Components: Store
> Affects Versions: 10.4.0.0
> Environment: all
> Reporter: Anurag Shekhar
> Assignee: Anurag Shekhar
> Attachments: BTreeController.diff, derby-3330-testcase.diff,
> derby-3330.diff, derby-3330v2.diff, derby-3330v3.diff, derby-3330v4.diff,
> derby-3330v5.diff, FunctionalSpec_DERBY-3330-V2.html,
> FunctionalSpec_DERBY-3330.html, UniqueConstraint_Implementation.html
>
>
> Allow unique constraint over nullable field. Right now derby support unique
> constraint only over not null columns.
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