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https://issues.apache.org/jira/browse/CASSANDRA-9673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14626143#comment-14626143
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Stefania commented on CASSANDRA-9673:
-------------------------------------

[~iamaleksey] do we also need a BATCH_RESPONSE verb or should we just keep on 
using REQUEST_RESPONSE? I've added BATCH_RESPONSE but it is functionally 
identical to REQUEST_RESPONSE. The same goes for the handler, 
WriteResponseHandler, which I have not duplicated instead. Another question is 
whether we need to introduce a new stage or is it OK to keep on using 
Stage.MUTATION?

I started writing dtest to check that we can still support older nodes, e.g. 
2.2, but things are quite broken at the moment, for example in ReadCommand 
serializer:

{code}
if (version < MessagingService.VERSION_30)
    throw new UnsupportedOperationException();
{code}

cc [~slebresne] - do we already have a ticket or plan for fixing compatibility 
with older nodes?


> Improve batchlog write path
> ---------------------------
>
>                 Key: CASSANDRA-9673
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9673
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Aleksey Yeschenko
>            Assignee: Stefania
>             Fix For: 3.0.0 rc1
>
>
> Currently we allocate an on-heap {{ByteBuffer}} to serialize the batched 
> mutations into, before sending it to a distant node, generating unnecessary 
> garbage (potentially a lot of it).
> With materialized views using the batchlog, it would be nice to optimise the 
> write path:
> - introduce a new verb ({{Batch}})
> - introduce a new message ({{BatchMessage}}) that would encapsulate the 
> mutations, expiration, and creation time (similar to {{HintMessage}} in 
> CASSANDRA-6230)
> - have MS serialize it directly instead of relying on an intermediate buffer
> To avoid merely shifting the temp buffer to the receiving side(s) we should 
> change the structure of the batchlog table to use a list or a map of 
> individual mutations.



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