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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-532) Support deferrable constraints
Date Mon, 12 Aug 2013 13:48:48 GMT

    [ https://issues.apache.org/jira/browse/DERBY-532?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13736869#comment-13736869
] 

Dag H. Wanvik commented on DERBY-532:
-------------------------------------

With the two patches above are finalized, I should be able to start thinking about actually
deferring the constraints. As a first step, I'll try to understand how to add machinery for
checking constraints at commit time, rather than at statement execution time, maybe for a
check constraint by disabling it (or dropping it if it comes into play during execution) first
and then checking all rows with a select like what is done when adding a check constraint.
In general I'd want to implement a naive approach first and the later try to do something
performant. Perhaps for small tables a naive approach could even be faster; time will tell.
                
> Support deferrable constraints
> ------------------------------
>
>                 Key: DERBY-532
>                 URL: https://issues.apache.org/jira/browse/DERBY-532
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Jörg von Frantzius
>            Assignee: Dag H. Wanvik
>              Labels: derby_triage10_11
>         Attachments: deferredConstraints.html, deferredConstraints.html, derby-532-syntax-binding-dict-1.diff,
derby-532-syntax-binding-dict-1.status, derby-532-syntax-binding-dict-2.diff, derby-532-syntax-binding-dict-2.status
>
>
> In many situations it is desirable to have constraints checking taking place only at
transaction commit time, and not before. If e.g. there is a chain of foreign key constraints
between tables, insert statements have to be ordered to avoid constraint violations. If foreign
key references are circular, the DML has to be split into insert statements and subsequent
update statements by the user.
> In other words, with deferred constraints checking, life is much easier for the user.
Also it can create problems with softwares such as object-relational mapping tools that are
not prepared for statement ordering and thus depend on deferred constraints checking.

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