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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-12042) Decouple messaging protocol versioning from individual message types
Date Tue, 21 Jun 2016 01:39:57 GMT
Aleksey Yeschenko created CASSANDRA-12042:
---------------------------------------------

             Summary: Decouple messaging protocol versioning from individual message types
                 Key: CASSANDRA-12042
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12042
             Project: Cassandra
          Issue Type: Improvement
          Components: Streaming and Messaging
            Reporter: Aleksey Yeschenko
            Priority: Blocker
             Fix For: 4.0


At the moment we have a single constant - {{MessagingService.current_version}} defining serialization
format for *everything*, including every possible message type.

In practice it means that any tiniest change to any message requires bumping the global {{MessagingService}}
version.

This is problematic for several reasons, the primary of which is currently the schema propagation
barrier between differently versioned C* nodes. In tick-tock world, it means that any change
(say, to a read command message), would require a messaging service bump, putting nodes on
split versions of the service, and making schema changes during this now considered minor
upgrade, impossible, which is not neat.

I propose that starting with 4.0 we version all messages individually instead, and separately
version messaging service protocol itself - which will basically amount to just framing, once
CASSANDRA-8457 is completed.

In practice, this might be implemented the following way:

# We use an extra byte with each message to specify the version of that particular message
type encoding
# Instead of relying on messaging service of the sending note (determining which can be racy,
especially during upgrades), we use that byte to determine the version of the message during
deserialisation
# On sending side, we can use the gossipped version of Cassandra itself - not the messaging
service version - to determine the maximum supported message type version of the destination
node

In the new world, I expect the framing protocol version to change very rarely after 4.0, if
ever, and most message types to change extremely rarely as well, with schema, read, and write
messages to change version most often.



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