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https://issues.apache.org/jira/browse/CASSANDRA-18546?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stefan Miklosovic updated CASSANDRA-18546:
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Summary: Remove unnecessary shuffling of GossipDigests in
Gossiper#makeRandomGossipDigest (was: Remove Gossiper#makeRandomGossipDigest)
> Remove unnecessary shuffling of GossipDigests in
> Gossiper#makeRandomGossipDigest
> --------------------------------------------------------------------------------
>
> Key: CASSANDRA-18546
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18546
> Project: Cassandra
> Issue Type: Improvement
> Components: Cluster/Gossip
> Reporter: Cameron Zemek
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 4.0.x, 4.1.x, 5.x
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> In going through trying to understand the Gossiper code I come across:
> {code:java}
> /**
> * The gossip digest is built based on randomization
> * rather than just looping through the collection of live endpoints.
> *
> * @param gDigests list of Gossip Digests.
> */
> private void makeRandomGossipDigest(List<GossipDigest> gDigests) {code}
> But I couldn't see what purpose randomization had. In fact in 3.11 it will
> call:
> {code:java}
> doSort(gDigestList); {code}
> On the receiving end, negating the purpose of the randomization.
>
> In discussion with [~stefan.miklosovic] he found this ticket CASSANDRA-14174
> So it seems to me this randomization may have been to allow for limited sizes
> of SYN messages. But this feature doesn't exist and as such by randomizing it
> is:
> * creating more garbage
> * using more CPU (sure its mostly trival; see next point)
> * more time spent on unnecessary functionality on the *single threaded*
> gossip stage.
> * complicating the code and making it more difficult to understand
> In fact there is a bug in the implementation:
> {code:java}
> int generation = 0;
> int maxVersion = 0; // local epstate will be part of
> endpointStateMap
> List<InetAddress> endpoints = new
> ArrayList<InetAddress>(endpointStateMap.keySet());
> Collections.shuffle(endpoints, random);
> for (InetAddress endpoint : endpoints)
> {
> epState = endpointStateMap.get(endpoint);
> if (epState != null)
> {
> generation = epState.getHeartBeatState().getGeneration();
> maxVersion = getMaxEndpointStateVersion(epState);
> }
> gDigests.add(new GossipDigest(endpoint, generation, maxVersion));
> } {code}
> If epState is null and we already had a non-null epState, then the next
> digest will use the generation and maxVersion of the previous iterated
> epState.
>
> Here is change to remove this randomization and fix the above bug,
> [https://github.com/apache/cassandra/pull/2357/commits/1ba422ab5de35f7057c7621ec3607dcbca19768c]
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