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https://issues.apache.org/jira/browse/QPID-5139?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alan Conway updated QPID-5139:
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Status: Ready To Review (was: In Progress)
> HA transactions block a thread, can deadlock the broker.
> --------------------------------------------------------
>
> Key: QPID-5139
> URL: https://issues.apache.org/jira/browse/QPID-5139
> Project: Qpid
> Issue Type: Bug
> Components: C++ Clustering
> Affects Versions: 0.24
> Reporter: Alan Conway
> Assignee: Alan Conway
> Priority: Critical
> Fix For: 0.25
>
>
> When the client sends a "prepare" command for a transaction, the thread
> handling that command is blocked until all backups have responded with their
> prepare status. This can easily deadlock the broker if there are more
> concurrent transactions than worker threads.
> To reproduce you need a way to delay completion of a transaction. The
> following regression test illustrates, it will be added to TransactionTests
> in ha_tests.py as part of the fix:
> def test_tx_block_threads(self):
> """Verify that TXs blocked in commit don't block broker threads."""
> cluster = HaCluster(self, 2, args=["--worker-threads=2"])
> sessions = [cluster[0].connect().session(transactional=True) for i in
> xrange(2)]
> for s in sessions: s.sender("foo;{create:always}").send("foo")
> self.assertEqual(2, len(cluster[1].agent().tx_queues()))
> os.kill(cluster[1].pid, signal.SIGSTOP) # Freeze backup so tx can't
> complete.
> threads = [ Thread(target=s.commit) for s in sessions]
> for t in threads: t.start()
> cluster[0].ready(timeout=1) # Should not block
> os.kill(cluster[1].pid, signal.SIGCONT) # Allow tx to complete.
> for t in threads: t.join()
> c.close()
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