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https://issues.apache.org/jira/browse/DERBY-4279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881103#action_12881103
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Kristian Waagan commented on DERBY-4279:
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The tinderbox test failed again with the following error in StressTestMulti:
2010-06-21 16:02:44.542 GMT Thread[DRDAConnThread_1289,5,derby.daemons] (XID =
1929067), (SESSIONID = 61), (DATABASE = wombat), (DRDAID =
NF000001.P530-869193450946392963{30}), Failed Statement is: null
java.lang.NullPointerException
at
org.apache.derby.impl.jdbc.EmbedPreparedStatement.getMetaData(Unknown Source)
at org.apache.derby.impl.drda.DRDAConnThread.writeSQLDARD(Unknown
Source)
at org.apache.derby.impl.drda.DRDAConnThread.processCommands(Unknown
Source)
at org.apache.derby.impl.drda.DRDAConnThread.run(Unknown Source)
It looks suspicious that after the change from returning void to returning a
PreparedStatement, the return value is ignored in
EmbedPreparedStatement.getMetaData. Is this correct?
As for the error itself, it has already been reported (DERBY-3823).
> 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: 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 prepared statement becomes out-of-date.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 After some time, the prepared statement becomes invalid or out-of-date for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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