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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4279) Statement cache deadlock
Date Mon, 28 Jun 2010 09:24:51 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12883081#action_12883081
] 

Kristian Waagan commented on DERBY-4279:
----------------------------------------

Another error. I was trying to get a stack trace with line numbers for the getMetaData error,
but this popped up instead.

[Error/failure logged at Sat Jun 26 06:04:57 CEST 2010]
junit.framework.AssertionFailedError: Caused by: 
java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
        at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:95)
        at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:142)
        at org.apache.derby.impl.jdbc.Util.javaException(Util.java:299)
        at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(TransactionResourceImpl.java:403)
        at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(TransactionResourceImpl.java:346)
        at org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConnection.java:2269)
        at org.apache.derby.impl.jdbc.ConnectionChild.handleException(ConnectionChild.java:81)
        at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:614)
        at org.apache.derby.impl.jdbc.EmbedStatement.executeQuery(EmbedStatement.java:152)
        at org.apache.derbyTesting.functionTests.tests.multi.StressMultiTest$StressMultiRunnable.select(StressMultiTest.java:555)
        at org.apache.derbyTesting.functionTests.tests.multi.StressMultiTest$StressMultiRunnable.run(StressMultiTest.java:429)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
        at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:45)
        at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(SQLExceptionFactory40.java:119)
        at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:70)
        ... 11 more
Caused by: java.lang.NullPointerException
        at org.apache.derby.impl.sql.GenericActivationHolder.<init>(GenericActivationHolder.java:129)
        at org.apache.derby.impl.sql.GenericPreparedStatement.getActivation(GenericPreparedStatement.java:257)
        at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:609)
        ... 4 more

        at org.apache.derbyTesting.functionTests.tests.multi.StressMultiTest.handleException(StressMultiTest.java:351)
        at org.apache.derbyTesting.functionTests.tests.multi.StressMultiTest.access$200(StressMultiTest.java:70)
        at org.apache.derbyTesting.functionTests.tests.multi.StressMultiTest$StressMultiRunnable.run(StressMultiTest.java:445)
        at java.lang.Thread.run(Thread.java:619)


> Statement cache deadlock
> ------------------------
>
>                 Key: DERBY-4279
>                 URL: https://issues.apache.org/jira/browse/DERBY-4279
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.0.2.1, 10.1.3.1, 10.2.2.0, 10.3.3.0, 10.4.2.0, 10.5.1.1
>         Environment: Windows Vista
>            Reporter: Jeff Stuckman
>            Assignee: Brett Wooldridge
>             Fix For: 10.7.0.0
>
>         Attachments: client_stacktrace_activation_closed.txt, Derby4279.java, patch4279.txt,
stacktrace.txt
>
>
> Due to a design flaw in the statement cache, a deadlock can occur if a prepared statement
becomes out-of-date.
> I will illustrate this with the following example:
> The application is using the embedded Derby driver. The application has two threads,
and each thread uses its own connection.
> There is a table named MYTABLE with column MYCOLUMN.
> 1. A thread prepares and executes the query SELECT MYCOLUMN FROM MYTABLE. The prepared
statement is stored in the statement cache (see org.apache.derby.impl.sql.GenericStatement
for this logic)
> 2. After some time, the prepared statement becomes invalid or out-of-date for some reason
(see org.apache.derby.impl.sql.GenericPreparedStatement)
> 3. Thread 1 begins a transaction and executes LOCK TABLE MYTABLE IN EXCLUSIVE MODE
> 4. Thread 2 begins a transaction and executes SELECT MYCOLUMN FROM MYTABLE. The statement
is in the statement cache but it is out-of-date. The thread begins to recompile the statement.
To compile the statement, the thread needs a shared lock on MYTABLE. Thread 1 already has
an exclusive lock on MYTABLE. Thread 2 waits.
> 5. Thread 1 executes SELECT MYCOLUMN FROM MYTABLE. The statement is in the statement
cache but it is being compiled. Thread 1 waits on the statement's monitor.
> 6. We have a deadlock. Derby eventually detects a lock timeout, but the error message
is not descriptive. The stacks at the time of the deadlock are:
> This deadlock is unique because it can still occur in a properly designed database. You
are only safe if all of your transactions are very simple and cannot be interleaved in a sequence
that causes the deadlock, or if your particular statements do not require a table lock to
compile. (For the sake of simplicity, I used LOCK TABLE in my example, but any UPDATE statement
would fit.)

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