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https://issues.apache.org/jira/browse/CASSANDRA-5632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13686809#comment-13686809
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Hayato Shimizu commented on CASSANDRA-5632:
-------------------------------------------
The patch fixes the issue of bandwidth-saving.
However, there seems to be two regressive issues being introduced.
1. Secondary DC coordinator node is always the same node. This introduces a
bottleneck in the secondary DC.
2. When using cqlsh, with EACH_QUORUM/ALL, with tracing on, on a row insert,
RPC timeout occurs from a node that is not verifiable in the trace output.
Trace output has been attached for a 6 node cluster, DC1:3, DC2:3 replication
factor configuration. network-topology configuration is also attached for
clarity.
> Cross-DC bandwidth-saving broken
> --------------------------------
>
> Key: CASSANDRA-5632
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5632
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.2.0
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Fix For: 1.2.6
>
> Attachments: 5632.txt, cassandra-topology.properties,
> fix_patch_bug.log
>
>
> We group messages by destination as follows to avoid sending multiple
> messages to a remote datacenter:
> {code}
> // Multimap that holds onto all the messages and addresses meant for
> a specific datacenter
> Map<String, Multimap<Message, InetAddress>> dcMessages
> {code}
> When we cleaned out the MessageProducer stuff for 2.0, this code
> {code}
> Multimap<Message, InetAddress> messages =
> dcMessages.get(dc);
> ...
>
> messages.put(producer.getMessage(Gossiper.instance.getVersion(destination)),
> destination);
> {code}
> turned into
> {code}
> Multimap<MessageOut, InetAddress> messages =
> dcMessages.get(dc);
> ...
> messages.put(rm.createMessage(), destination);
> {code}
> Thus, we weren't actually grouping anything anymore -- each destination
> replica was stored under a separate Message key, unlike under the old
> CachingMessageProducer.
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