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From "Kristian Waagan (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5603) EmbedConnection.clearLOBMapping() incorrectly clears lobFiles causing a ConcurrentModificationException
Date Mon, 06 Feb 2012 16:30:03 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201377#comment-13201377

Kristian Waagan commented on DERBY-5603:

Thank you for the feedback.

It's hard to say exactly what's going on without a repro, but:
  o the maps are private to each connection
  o the code you pointed at is obviously broken, and will fail if a map with more than one
entry is cleared
  o access to the map is synchronized on the connection object

Currently I can only think of the situation where the entries haven't been cleared the "normal"
way for whatever reason, and then the clearing fails due to the broken code.
I'll wait for more input from the community, and then commit a patch along the lines of the
current suggestion/patch if nothing substantial comes up.

Finally, how often do you see this bug?
Are you running with isolation level read-uncommitted? (may not be relevant, but there are
some issues with LOBs and locking at that level)
Are you in a situation where you could test a build off the head of the 10.8 branch?
That is, + all fixes that have been backported since the release. Building the jars
with + this fix only is also possible of course. None of these have been tested thoroughly
by the community.

> EmbedConnection.clearLOBMapping() incorrectly clears lobFiles causing a ConcurrentModificationException
> -------------------------------------------------------------------------------------------------------
>                 Key: DERBY-5603
>                 URL: https://issues.apache.org/jira/browse/DERBY-5603
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC
>    Affects Versions:,
>         Environment: Win 7 64 bit
> JDK 1.6.0_24
>            Reporter: Jon Steinich
>            Assignee: Kristian Waagan
>            Priority: Critical
>         Attachments: derby-5603-1a-avoid_concurrentmodification.diff
>   Original Estimate: 1h
>  Remaining Estimate: 1h
> In EmbedConnection.clearLOBMapping()  the code which iterates over lobFiles has a finally
block which clears the Set.  This causes a ConcurrentModificationException to be thrown and
even using a concurrent data structure would still result in only one LOBFile being correctly
> This will occur anytime the lobFiles Set contains more than 1 LOBFile.
> Stack Trace:
> java.sql.SQLException: Java exception: ': java.util.ConcurrentModificationException'.

>  at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown Source)

>  at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source) 
>  at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source) 
>  at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown Source)

>  at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown Source)

>  at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown Source) 
>  at org.apache.derby.impl.jdbc.EmbedConnection.commit(Unknown Source) 
> <lines removed>
> Caused by: java.sql.SQLException: Java exception: ': java.util.ConcurrentModificationException'.

>  at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source) 
>  at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown
>  ... 16 more 
> Caused by: java.util.ConcurrentModificationException 
>  at java.util.HashMap$HashIterator.nextEntry(Unknown Source) 
>  at java.util.HashMap$KeyIterator.next(Unknown Source) 
>  at org.apache.derby.impl.jdbc.EmbedConnection.clearLOBMapping(Unknown Source) 
>  ... 10 more

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