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https://issues.apache.org/jira/browse/DERBY-4279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422261#comment-13422261
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Kristian Waagan commented on DERBY-4279:
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>From what I can see, the lock, which is a "container intention read lock"
>(CIS), is released as soon as the controller is closed. I observed this by
>tracing the locks (derby.debug.true=LockTrace + a custom message to the log to
>navigate in derby.log). This is a very short time-span, and it happens
>independently of the isolation level of the transaction (separate
>sub-transaction for compilation?). Once my test-run has completed I will
>commit the patch.
If we observe the deadlock also when the mode is DDL_MODE I don't see why we
can't use NO_LOCK in all cases, since the code appears to be prepared to handle
that the conglomerate is dropped under its feet. However, it seems safer to me
to keep the change minimal for the time being.
> 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, 10.8.1.2
> Environment: Windows Vista, OS X 10.5+
> Reporter: Jeff Stuckman
> Labels: derby_triage10_5_2
> Attachments: Derby4279.java, client_stacktrace_activation_closed.txt,
> no-lock-experiment.diff, patch4279.txt, patch4279_2.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 prepared statement becomes out-of-date.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 After some time, the prepared statement becomes invalid or out-of-date for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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