[jira] [Commented] (CASSANDRA-9673) Improve batchlog write path

["Aleksey Yeschenko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-9673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660112#comment-14660112 ] 

Aleksey Yeschenko commented on CASSANDRA-9673:
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[~Stefania] Now that CASSANDRA-7237 has been resolved, can you reapply the patch on top of latest cassandra-3.0? This will be more difficult than a regular rebase.

CASSANDRA-6477 intervened with MS verbs for batchlog, and CASSANDRA-7237 added the new table. In addition to compatibility measures in your existing patch, we now also need to intercept mutations for the old batchlog table and properly convert them to mutations for the new table, with the new structure.

> 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
>
>         Attachments: 9673_001.tar.gz, 9673_004.tar.gz, gc_times_first_node_patched_004.png, gc_times_first_node_trunk_004.png
>
>
> 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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