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https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14504158#comment-14504158
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Benedict edited comment on CASSANDRA-8789 at 4/21/15 2:05 AM:
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2.0 stress, AFAICR, does not load balance. By default 2.1 does (smart thrift
routing round-robins the owning nodes for any token). So all of the writes to
the cluster are likely being piped through a single node in the 2.0 experiment
(so over just two tcp connections), instead of evenly spread all three (i.e.
six tcp connections).
was (Author: benedict):
2.0 stress, AFAICR, does not load balance. By default 2.1 does (smart thrift
routing round-robins the owning nodes for any token). So all of the writes to
the cluster are likely being piped through a single node in the 2.0 experiment
(so over just two tcp connections), instead of evenly spread over six.
> OutboundTcpConnectionPool should route messages to sockets by size not type
> ---------------------------------------------------------------------------
>
> Key: CASSANDRA-8789
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8789
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Ariel Weisberg
> Assignee: Ariel Weisberg
> Fix For: 3.0
>
> Attachments: 8789.diff
>
>
> I was looking at this trying to understand what messages flow over which
> connection.
> For reads the request goes out over the command connection and the response
> comes back over the ack connection.
> For writes the request goes out over the command connection and the response
> comes back over the command connection.
> Reads get a dedicated socket for responses. Mutation commands and responses
> both travel over the same socket along with read requests.
> Sockets are used uni-directional so there are actually four sockets in play
> and four threads at each node (2 inbounded, 2 outbound).
> CASSANDRA-488 doesn't leave a record of what the impact of this change was.
> If someone remembers what situations were made better it would be good to
> know.
> I am not clear on when/how this is helpful. The consumer side shouldn't be
> blocking so the only head of line blocking issue is the time it takes to
> transfer data over the wire.
> If message size is the cause of blocking issues then the current design mixes
> small messages and large messages on the same connection retaining the head
> of line blocking.
> Read requests share the same connection as write requests (which are large),
> and write acknowledgments (which are small) share the same connections as
> write requests. The only winner is read acknowledgements.
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