capistrant commented on code in PR #20155:
URL: https://github.com/apache/druid/pull/20155#discussion_r3866760755
##########
server/src/main/java/org/apache/druid/server/coordinator/loading/StrategicSegmentAssigner.java:
##########
@@ -538,6 +548,30 @@ private int loadPartialReplicas(
return numLoadsQueued;
}
+ /**
+ * Orders {@code eligibleServers} into the sequence a load should try them
in: round robin across the tier when
+ * round-robin assignment is enabled, else by the balancer strategy.
+ * <p>
+ * The round-robin branch ignores {@code eligibleServers} and derives its
candidates from the tier, keeping those
+ * that pass {@link ServerHolder#canLoadSegment} at the moment each one is
taken. Callers pass their complete
+ * eligible set: the two branches otherwise disagree on which servers a load
may target, and an empty
+ * {@code eligibleServers} does not imply an empty iterator.
+ * <p>
+ * Consume the result lazily. {@link RoundRobinServerSelector} advances a
per-tier cursor on every element taken, so
+ * draining the iterator for a segment that needs one replica advances the
cursor a full lap and hands the next
+ * segment the same starting server.
+ */
+ private Iterator<ServerHolder> serversToLoadSegment(
+ DataSegment segment,
+ String tier,
+ List<ServerHolder> eligibleServers
+ )
+ {
+ return useRoundRobinAssignment
+ ? serverSelector.getServersInTierToLoadSegment(tier, segment)
Review Comment:
I'm going to address this in a follow up via the queue-budget accounting
change after cancelation. This case is only impacting when not using smart
segment balancing which has been the default in druid for some time. I agree
that it makes sense to fix, but I'd like it to be reviewed separately. Will
cross llink PR once it is up.
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