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https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14510016#comment-14510016
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Benedict edited comment on CASSANDRA-8789 at 4/23/15 10:54 PM:
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I should clarify here that I do think MUTATION messages could plausibly delay
gossip messages where they couldn't before. However REQUEST_RESPONSE messages
as mentioned above as the potential cause could always cause head of line
blocking for gossip messages. So my position is only that the head of line
blocking concern is not a new one, not that its characteristics are identical.
I don't however have any data/position on what these theoretical analyses have
on the perceived issue.
was (Author: benedict):
I should clarify here that I do think MUTATION messages could plausibly delay
gossip messages where they couldn't before. However REQUEST_RESPONSE messages
as mentioned above as the potential cause could always cause head of line
blocking for gossip messages. So my position is only that the head of line
blocking concern is not a new one, not that its characteristics are identical.
> 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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