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https://issues.apache.org/jira/browse/DERBY-6510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13935037#comment-13935037
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Dyre Tjeldvoll commented on DERBY-6510:
---------------------------------------
On derby-dev I wrote:
??Alternatively, there could be some kind of poor synchronization/race
condition causing all the threads to start repreparing the query simultaneously
(for the same reason). So when the thread tries to acquire the lock, it is
blocked until the first thread has finished the long-lasting prepare, but when
it obtains the lock it does not detect that the reprepare is no longer needed
and proceeds with another (unecessary) long-lasting prepare.??
After reading the source I think I can debunk this theory. As the following
code snippet shows, the code does detect the siuation that the statement was
prepare by another thread while we waited for the lock:
{code:title=From GenericStatement.prepMinion(...)|borderStyle=solid}
synchronized (preparedStmt)
{
for (;;) {
if (foundInCache) {
if
(preparedStmt.referencesSessionSchema()) {
// cannot use this state since
it is private to a connection.
// switch to a new statement.
foundInCache = false;
preparedStmt = new
GenericPreparedStatement(this);
break;
}
}
// did it get updated while we waited for the
lock on it?
if (preparedStmt.upToDate()) {
return preparedStmt;
}
if (!preparedStmt.isCompiling()) {
break;
}
try {
preparedStmt.wait();
} catch (InterruptedException ie) {
InterruptStatus.setInterrupted();
}
}
preparedStmt.beginCompiling();
}
{code}
> Deby engine threads not making progress
> ---------------------------------------
>
> Key: DERBY-6510
> URL: https://issues.apache.org/jira/browse/DERBY-6510
> Project: Derby
> Issue Type: Bug
> Components: Network Server
> Affects Versions: 10.9.1.0
> Environment: Oracle Solaris 10/9, Oracle M5000 32 CPU, 128GB memory,
> 8GB allocated to Derby Network Server
> Reporter: Brett Bergquist
> Priority: Critical
> Attachments: dbstate.log, derbystacktrace.txt
>
>
> We had an issue today in a production environment at a large customer site.
> Basically 5 database interactions became stuck and are not progressing.
> Part of the system dump performs a stack trace every few seconds for a period
> of a minute on the Glassfish application server and the Derby database engine
> (running in network server mode). Also, the dump captures the current
> transactions and the current lock table (ie. syscs_diag.transactions and
> syscs_diag.lock_table). We had to restart the system and in doing so, the
> Derby database engine would not shutdown and had to be killed.
> The stack traces of the Derby engine show 5 threads that are basically making
> no progress in that at each sample, they are at the same point, waiting.
> I will attach the stack traces as well as the state of the transactions and
> locks.
> Interesting is that the "derby.jdbc.xaTransactionTimeout =1800" is set, yet
> the transactions did not timeout. The timeout is for 30 minutes but the
> transactions were in process for hours.
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