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https://issues.apache.org/jira/browse/DERBY-3900?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kathey Marsden updated DERBY-3900:
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Component/s: SQL
> SELECT ... FOR UPDATE cannot be used in many queries
> ----------------------------------------------------
>
> Key: DERBY-3900
> URL: https://issues.apache.org/jira/browse/DERBY-3900
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Marco
>
> The documentation in
> http://db.apache.org/derby/docs/10.4/ref/rrefsqlj41360.html#rrefsqlj41360__sqlj15384
> says that SELECT ... FOR UPDATE cannot be used in many situations (e.g. when
> ORDER BY is present or when JOINs are used). I can very well understand that
> the current implementation using updatable cursors is very hard to implement
> when multiple tables are used and therefore these restrictions are probably
> necessary.
> However, besides that functionality, "FOR UPDATE" is extremely useful for
> transactional integrity: For example, we - http://www.jfire.org - use
> transaction isolation level read committed, because it provides good
> transaction safety combined with good performance. When modifying records, we
> first select the appropriate table rows with a SELECT FOR UPDATE in order to
> guarantee that the data we just read cannot be manipulated by another
> transaction while we are working with it.
> I do not see any reason why this locking behaviour should not be possible for
> certain queries. Therefore, I recommend to introduce a configuration setting
> (maybe a system property? or an option passed to the JDBC-URL?) that disables
> updatable queries completely (we don't need them anyway and probably it
> improves performance when not using them). With this option set, the SELECT
> ... FOR UPDATE should solely affect locks on rows - and work with all SELECT
> expressions - no matter whether they use JOIN, UNION, ORDER BY etc..
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