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Date: Wed, 12 Aug 2015 09:22:46 +0000 (UTC)
From: "Stefania (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (CASSANDRA-9673) Improve batchlog write path
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    [ https://issues.apache.org/jira/browse/CASSANDRA-9673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14693202#comment-14693202 ] 

Stefania commented on CASSANDRA-9673:
-------------------------------------

[~iamaleksey] I still need to do mixed version testing and check the CI results but the rebase on 3.0 and the changes you requested are available for review if you want to speed things up. Else I'll post another update when the tests are complete.

I've left you a question in SS with a TODO, I am no sure why in {{mutateMV}} we insert a batch mutation containing all mutations, for every single mutation, it seems wrong to me.

For replaying legacy mutations, I've opted for a conversion done before replaying, which is not very efficient, but keeps the code clean. I figured mixed version clusters are transient but if it concerns you I can enhance it.

> 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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