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From "Jon Steinich (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5603) EmbedConnection.clearLOBMapping() incorrectly clears lobFiles causing a ConcurrentModificationException
Date Mon, 06 Feb 2012 15:17:59 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201341#comment-13201341

Jon Steinich commented on DERBY-5603:

Ah, I didn't realize they were generally removed prior to that point.  Now something that
seemed irrelevant before is likely the key...
We have 2 connections open to the database; one for reading and one for writing.  The read
connection is probably reading in a blob (creating one) while the commit is clearing on the
write connection.

It wasn't under high load or low memory when the error occurred.  We always call createBlob()
and then write to its output stream.
> 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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