enhance HBase RPC to support free-ing up server handler threads even if
response is not ready
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Key: HBASE-3899
URL: https://issues.apache.org/jira/browse/HBASE-3899
Project: HBase
Issue Type: Improvement
Components: ipc
Reporter: dhruba borthakur
Assignee: dhruba borthakur
In the current implementation, the server handler thread picks up an item from
the incoming callqueue, processes it and then wraps the response as a Writable
and sends it back to the IPC server module. This wastes thread-resources when
the thread is blocked for disk IO (transaction logging, read into block cache,
etc).
It would be nice if we can make the RPC Server Handler threads pick up a call
from the IPC queue, hand it over to the application (e.g. HRegion), the
application can queue it to be processed asynchronously and send a response
back to the IPC server module saying that the response is not ready. The RPC
Server Handler thread is now ready to pick up another request from the incoming
callqueue. When the queued call is processed by the application, it indicates
to the IPC module that the response is now ready to be sent back to the client.
The RPC client continues to experience the same behaviour as before. A RPC
client is synchronous and blocks till the response arrives.
This RPC enhancement allows us to do very powerful things with the
RegionServer. In future, we can make enhance the RegionServer's threading model
to a message-passing model for better performance. We will not be limited by
the number of threads in the RegionServer.
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