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Type: Bug
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Resolution: Fixed
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Priority: Critical - P2
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Affects Version/s: 3.6.4
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Component/s: Networking
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None
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Fully Compatible
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ALL
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v3.6
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Platforms 2018-04-23, Platforms 2018-05-07
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0
- The AsyncRequestsSender holds a lock during construction and work scheduling.
- This lock prevents callbacks from running if their response comes back during scheduling.
- Scheduling can take a long time (up to 20 seconds per shard) if a read preference cannot be satisfied. This is done by a blocking call into the ReplicaSetMonitor
The bad sequence of events is:
- Scatter gather request to two shards is dispatched
- The first host suceeds in targetting and runs
- The second host cannot satisfy it's read pref, blocking holding a lock
- The first request suceeds, blocking in running _handleResponse
If you have enough of those, you can saturate all background networking workers, making your mongos completely unresponsive until targeting can succeed.
- related to
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SERVER-35167 AsyncResultsMerger can block networking threads in callbacks
- Closed