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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-5121) Data corruption when executing an UPDATE trigger
Date Mon, 14 Mar 2011 21:42:29 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13006651#comment-13006651

Mamta A. Satoor commented on DERBY-5121:

Frist of all, thanks so much for having such an easy reproducible test case. 

I looked at the generated code for the trigger action and see the problem Rick described.
The purpose of DERBY-1482 was to avoid reading the columns that are not needed by the trigger
action, especially the LOB columns which could result in OOM problems. The code that I added
for DERBY-1482 looked at the columns referenced in trigger action and *assumed* that the resultset
would have just those columns during the trigger execution time. So, in following example,
the trigger action references only 2 out of the 3 columns, the 1st and the 3rd column. The
trigger action thus assumes that the resultset would have just columns 1 and 3 in the resultset's
column positions 1 and 2. But it did not take into account where the triggering SQL might
need additional columns of it's own. In the given example, the triggering UPDATE statement
is using the column in position 2 from the trigger table and this causes the trigger action
to start using the columns in incorrect column positions.

I understand the urgency of this jira and based on that, I will see if I can disable the optimization
introduced by DERBY-1482. Once that is done, I will look into what could be other ways to
solve the unnecessary column reads algorithm. One thing that comes to my mind is to may be
read all the columns upto the highest column position required by the trigger action. So in
our eg, triggeredCorruption.sql, the trigger action is looking at column positions 1 and 3
and hence we should read columns 1, 2 and 3 even though the trigger action does not need the
column 2. Any columns after the highest column position required by the trigger action will
be read if the triggering SQL requires it but it will not affect the column positions getting
used inside the trigger action.

I will also think of any other possible way to tackle the column reading optimization. If
anyone has any other ideas, please let me know.

> Data corruption when executing an UPDATE trigger
> ------------------------------------------------
>                 Key: DERBY-5121
>                 URL: https://issues.apache.org/jira/browse/DERBY-5121
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:,
>            Reporter: Rick Hillegas
>            Assignee: Mamta A. Satoor
>              Labels: derby_triage10_8
>         Attachments: DummyProc.java, triggerBug.sql, triggerBug.sql, triggeredCorruption.sql
> When executing an UPDATE trigger, the following error is raised. I will attach a test
> ERROR XCL12: An attempt was made to put a data value of type 'org.apache.derby.impl.jdbc.EmbedClob'
into a data value of type 'INTEGER'.

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