Christian Esken created CASSANDRA-13265:
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Summary: Communication breakdown in OutboundTcpConnection
Key: CASSANDRA-13265
URL: https://issues.apache.org/jira/browse/CASSANDRA-13265
Project: Cassandra
Issue Type: Bug
Environment: Cassandra 3.0.9
Java HotSpot(TM) 64-Bit Server VM version 25.112-b15 (Java version
1.8.0_112-b15)
Linux 3.16
Reporter: Christian Esken
I observed that sometimes a single node in a Cassandra cluster fails to
communicate to the other nodes. This can happen at any time, during peak load
or low load. Restarting that single node from the cluster fixes the issue.
Before going in to details, I want to state that I have analyzed the situation
and am already developing a possible fix. Here is the analysis so far:
- A Threaddump in this situation showed that 324 Threads in the
OutboundTcpConnection class wanted to lock the backlog queue for doing
expiration.
- A class histogram shows 262508 instances of
OutboundTcpConnection$QueuedMessage.
What is the effect of it? As soon as the Cassandra node has reached that state,
it never gets out of it by itself, it is thrashing itself to death instead, as
each of the Thread fully locks the Queue for reading and writing by calling
iterator.next().
- Writing: Only after 262508 locking operation it can progress with actually
writing to the Queue.
- Reading: Is also blocked, as 324 Threads try to do iterator.next(), and fully
lock the Queue
This means: Writing blocks the Queue for reading, and readers might even be
starved which makes the situation even worse.
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The setup is:
- 3-node cluster
- replication factor 2
- Consistency LOCAL_ONE
- No remote DC's
- high write throughput (100000 INSERT statements per second and more during
peak times).
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