[CASSANDRA-1358] Clogged RRS/RMS stages can hold up processing of gossip messages and request acks

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 0.6.5

Environment

All.

• Assignee: Jonathan Ellis
• Reporter: Mike Malone

Authors

Jonathan Ellis

• Created: 04/Aug/10 18:12
• Updated: 16/Apr/19 09:33
• Resolved: 13/Aug/10 17:10

Description

The message deserialization process can become a bottleneck that prevents efficient resource utilization because the executor that manages the deserialization process will never grow beyond a single thread. The message deserializer executor is instantiated in the MessagingService constructor as a JMXEnableThreadPoolExecutor, which extends java.util.concurrent.ThreadPoolExecutor. The thread pool is instantiated with a corePoolSize of 1 and a maximumPoolSize of Runtime.getRuntime().availableProcessors(). But, according to the ThreadPoolExecutor documentation "using an unbounded queue (for example a LinkedBlockingQueue without a predefined capacity) will cause new tasks to be queued in cases where all corePoolSize threads are busy. Thus, no more than corePoolSize threads will ever be created. (And the value of the maximumPoolSize therefore doesn't have any effect.)"

The message deserializer pool uses a LinkedBlockingQueue, so there will never be more than one deserialization thread. This issue became a problem in our production cluster when the MESSAGE-DESERIALIZER-POOL began to back up on a node that was only lightly loaded. We increased the core pool size to 4 and the situation improved, but the deserializer pool was still backing up while the machine was not fully utilized (less than 100% CPU utilization). This leads me to think that the deserializer thread is blocking on some sort of I/O, which seems like it shouldn't happen.