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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2321) Support RPC interface changes at runtime
Date Sun, 14 Mar 2010 00:58:27 GMT
Support RPC interface changes at runtime

                 Key: HBASE-2321
                 URL: https://issues.apache.org/jira/browse/HBASE-2321
             Project: Hadoop HBase
          Issue Type: Improvement
            Reporter: Andrew Purtell
             Fix For: 0.21.0

Now we are able to append methods to interfaces without breaking RPC compatibility with earlier
releases. However there is no way that I am aware of to dynamically add entire new RPC interfaces.
Methods/parameters are fixed to the class used to instantiate the server at that time. Coprocessors
need this. They will extend functionality on regions in arbitrary ways. How to support that
on the client side? A couple of options:

1. New RPC from scratch.

2. Modify HBaseServer such that multiple interface objects can be used for reflection and
objects can be added or removed at runtime. 

3. Have the coprocessor host instantiate new HBaseServer instances on ephemeral ports and
publish the endpoints to clients via Zookeeper. Couple this with a small modification to HBaseServer
to support elastic thread pools to minimize the number of threads that might be kept around
in the JVM. 

4. Add a generic method to HRegionInterface, an ioctl-like construction, which accepts a ImmutableBytesWritable
key and an array of Writable as parameters. 

My opinion is we should opt for #4 as it is the simplest and most expedient approach. I could
also do #3 if consensus prefers. Really we should do #1 but it's not clear who has the time
for that at the moment. 

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