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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-5926) The native protocol server can deadlock
Date Fri, 23 Aug 2013 11:57:52 GMT
Sylvain Lebresne created CASSANDRA-5926:
-------------------------------------------

             Summary: The native protocol server can deadlock
                 Key: CASSANDRA-5926
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5926
             Project: Cassandra
          Issue Type: Bug
            Reporter: Sylvain Lebresne
            Assignee: Sylvain Lebresne
             Fix For: 1.2.9


Until CASSANDRA-5239 (i.e. since StorageProxy is blocking), the native protocol server needs
to use a thread per request being processed. For that, it currently use a DebuggableThreadPoolExecutor,
but with a limited queue. The rational being that we don't want to OOM if a client overwhelm
the server. Rather, we prefer blocking (which DTPE gives us) on the submission of new request
by the netty worker threads when all threads are busy.

However, as it happens, when netty sends back a response to a query, there is cases where
some events (technically, InterestChanged and WriteComplete events) are send up the pipeline.
And those event are submitted on the request executor as other requests. Long story short,
a request thread can end blocking on the submission to its own executor, hence deadlocking.

The simplest solution is probably to reuse MemoryAwareThreadPoolExecutor from netty rather
that our own DTPE as it also allow to block task submission when all threads are busy but
knows not to block it's own internal events.


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