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https://issues.apache.org/jira/browse/CASSANDRA-14174?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16341709#comment-16341709
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Joel Knighton commented on CASSANDRA-14174:
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I took another look at this. I've still got nothing for a positive effect of
this code remaining, intentional or otherwise. CI looks good. The dtests are
admittedly noisy, but I don't see any problems that look like a result of this
change.
+1.
> Remove GossipDigestSynVerbHandler#doSort()
> ------------------------------------------
>
> Key: CASSANDRA-14174
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14174
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jason Brown
> Assignee: Jason Brown
> Priority: Minor
> Fix For: 4.x
>
>
> I have personally tripped up on this function a couple of times over the
> years, believing that it contributes to bugs in some way or another. While I
> have not found that (necessarily!) to be the case, I feel this function is
> completely useless in the grand scope of things.
> Going back through the mists of time (that is, {{git log}}), it appears this
> function was part of the original code drop from Facebook when they open
> sourced cassandra. Looking at the {{#doSort()}} method, all it does is sort
> the incoming list of {{GossipDigest}} s by the difference between the remote
> node's maxValue for a given peer and the local nodes' maxValue.
> The only universe where this is actually an optimization is if you go back
> and read the [Scuttlebutt
> paper|https://www.cs.cornell.edu/home/rvr/papers/flowgossip.pdf] (upon which
> cassandra's Gossip anti-entropy reconciliation is based). The end of section
> 3.2 describes ordering of the incoming digests such that, in the case where
> you do not return all of the differences (because you are optimizing for the
> return message size), you can gather the differences for the peers which are
> most of out sync. The ordering implemented in cassandra is the second
> ordering described in the paper, called "scuttle depth".
> As we always send all differences between two nodes (message size be damned),
> this optimization, borrowed from the paper, is largely irrelevant for
> Cassandra's purposes.
> Thus, I propose we remove this method for the following gains:
> - less garbage created
> - less CPU (sure, it's mostly trivial; see next point)
> - less time spent on unnecessary functionality on the *single threaded*
> gossip stage.
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