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https://issues.apache.org/jira/browse/CASSANDRA-19426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17821167#comment-17821167
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Stefan Miklosovic commented on CASSANDRA-19426:
-----------------------------------------------
in maybeGossipToSeed, this
{noformat}
double probability = seeds.size() / (double) (liveEndpoints.size() +
unreachableEndpoints.size());
{noformat}
will never be Infinity, because liveEndoints.size() will not be 0. If it was,
we would never came to that "else" branch.
If we have this in maybeGossipToCMS
{noformat}
Set<InetAddressAndPort> cms =
ClusterMetadata.current().fullCMSMembers();
if (cms.contains(getBroadcastAddressAndPort()))
return;
double probability = cms.size() / (double) (liveEndpoints.size() +
unreachableEndpoints.size());
{noformat}
cms set can be e.g. 2 nodes, if cms does not contain the current node, then
liveEndpoints will be non-zero too, no? In other words, can cms members be "not
live" ? If they are not live, then they will be unreachable, so that will again
not produce Infinity there.
I am still returning to this but I just can not see how it might be Infinity.
Both liveEndpoints and unreachableEndpoints would have to be 0. Under what
scenario that would be true?
> Fix Double Type issues in the Gossiper#maybeGossipToCMS
> -------------------------------------------------------
>
> Key: CASSANDRA-19426
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19426
> Project: Cassandra
> Issue Type: Improvement
> Components: Cluster/Gossip, Transactional Cluster Metadata
> Reporter: Ling Mao
> Assignee: Ling Mao
> Priority: Low
> Fix For: 5.x
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> _*issue-1:*_
> if liveEndpoints.size()=unreachableEndpoints.size()=0; probability will be
> {*}_Infinity_{*}.
> randDbl <= probability will always be true, then sendGossip
> _*issue-2:*_
> comparing two double is safe by using *<* or {*}>{*}. However missing
> accuracy will happen if we compare the equality of two double by
> intuition({*}={*}). For example:
> {code:java}
> double probability = 0.1;
> double randDbl = 0.10000000000000001; // Slightly greater than probability
> if (randDbl <= probability)
> {
> System.out.println("randDbl <= probability(always here)");
> }
> else
> {
> System.out.println("randDbl > probability");
> }
> {code}
> A good example from: _*Gossiper#maybeGossipToUnreachableMember*_
> {code:java}
> if (randDbl < prob)
> {
> sendGossip(message, Sets.filter(unreachableEndpoints.keySet(),
> ep ->
> !isDeadState(getEndpointStateMap().get(ep))));
> }{code}
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