lucasbru commented on code in PR #23784:
URL: https://github.com/apache/kafka/pull/23784#discussion_r4249733955
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/AssignmentRefinerImpl.java:
##########
@@ -237,12 +238,19 @@ static Map<String, ProcessLoad> indexProcessLoad(
*
* <p>Only an active-running or caught-up copy is ever promoted.
*
+ * <p>A task whose target owner is {@link WarmupSupport#NOT_SUPPORTED} is
never staged: its target owner never
+ * reports its restore progress, so no warm-up task could ever be seen to
complete the migration.
+ *
* @param currentAssignment
* The indexed current assignment, from {@link
#indexCurrentAssignment}.
* @param targetAssignment
* All members' target assignments, as computed by the task
assignor.
* @param members
* All members of the group, used to resolve which process a member
runs in.
+ * @param warmupSupport
+ * Whether each member may be handed a warm-up task.
+ * @param heartbeatVersions
+ * The version of the latest heartbeat of each member, which tells
whether a member can be warmed up.
Review Comment:
Fixed in 4df855bc67. There was only one such tag in the file.
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/AssignmentRefinerImpl.java:
##########
@@ -302,6 +308,15 @@ static TaskDecisions analyzeTasks(
continue;
}
+ // A target owner that never reports its restore progress could
not be seen to finish warming up, so the
+ // task is handed to it right away, cold unless its own process
still holds the state. A caught-up copy on
+ // another process is not worth a detour either: promoting it
would only postpone the same grant and add
+ // a second hand-over. This is the price of a group that is
part-way through a client upgrade.
+ if (WarmupSupport.of(heartbeatVersions.get(targetOwner)) ==
WarmupSupport.NOT_SUPPORTED) {
Review Comment:
Unknown versions after a failover are handled in a follow-up PR of this
series. It won't grant directly, though: right after a failover every member is
unknown, so granting would turn every pending migration into a cold hand-over.
Instead, while any member is unknown, the refiner keeps migrations staged and
funds no new warm-up tasks until every member has heartbeated.
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