ableegoldman commented on a change in pull request #10509:
URL: https://github.com/apache/kafka/pull/10509#discussion_r627019548
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File path:
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractStickyAssignor.java
##########
@@ -149,141 +149,210 @@ private boolean allSubscriptionsEqual(Set<String>
allTopics,
* This constrainedAssign optimizes the assignment algorithm when all
consumers were subscribed to same set of topics.
* The method includes the following steps:
*
- * 1. Reassign as many previously owned partitions as possible, up to the
maxQuota
- * 2. Fill remaining members up to minQuota
- * 3. If we ran out of unassigned partitions before filling all consumers,
we need to start stealing partitions
- * from the over-full consumers at max capacity
- * 4. Otherwise we may have run out of unfilled consumers before assigning
all partitions, in which case we
- * should just distribute one partition each to all consumers at min
capacity
+ * 1. Reassign previously owned partitions:
+ * a. if owned less than minQuota partitions, just assign all owned
partitions, and put the member into unfilled member list
+ * b. if owned maxQuota or more, and we're still under the number of
expected max capacity members, assign maxQuota partitions
+ * c. if owned at least "minQuota" of partitions, assign minQuota
partitions, and put the member into unfilled member list if
+ * we're still under the number of expected max capacity members
+ * 2. Fill remaining members up to the expected numbers of maxQuota
partitions, otherwise, to minQuota partitions
*
* @param partitionsPerTopic The number of partitions for each
subscribed topic
* @param consumerToOwnedPartitions Each consumer's previously owned and
still-subscribed partitions
*
- * @return Map from each member to the list of partitions assigned to them.
+ * @return Map from each member to the list of
partitions assigned to them.
*/
private Map<String, List<TopicPartition>> constrainedAssign(Map<String,
Integer> partitionsPerTopic,
Map<String,
List<TopicPartition>> consumerToOwnedPartitions) {
- SortedSet<TopicPartition> unassignedPartitions =
getTopicPartitions(partitionsPerTopic);
+ if (log.isDebugEnabled()) {
+ log.debug("performing constrained assign. partitionsPerTopic: {},
consumerToOwnedPartitions: {}",
+ partitionsPerTopic, consumerToOwnedPartitions);
+ }
Set<TopicPartition> allRevokedPartitions = new HashSet<>();
- // Each consumer should end up in exactly one of the below
- // the consumers not yet at capacity
+ // the consumers not yet at expected capacity
List<String> unfilledMembers = new LinkedList<>();
- // the members with exactly maxQuota partitions assigned
- Queue<String> maxCapacityMembers = new LinkedList<>();
- // the members with exactly minQuota partitions assigned
- Queue<String> minCapacityMembers = new LinkedList<>();
int numberOfConsumers = consumerToOwnedPartitions.size();
- int minQuota = (int) Math.floor(((double) unassignedPartitions.size())
/ numberOfConsumers);
- int maxQuota = (int) Math.ceil(((double) unassignedPartitions.size())
/ numberOfConsumers);
+ int totalPartitionsCount =
partitionsPerTopic.values().stream().reduce(0, Integer::sum);
+
+ int minQuota = (int) Math.floor(((double) totalPartitionsCount) /
numberOfConsumers);
+ int maxQuota = (int) Math.ceil(((double) totalPartitionsCount) /
numberOfConsumers);
+ // the expected number of members with maxQuota assignment
+ int expectedNumMembersHavingMorePartitions = totalPartitionsCount %
numberOfConsumers;
+ // the number of members with exactly maxQuota partitions assigned
+ int numMembersHavingMorePartitions = 0;
- // initialize the assignment map with an empty array of size minQuota
for all members
+ // initialize the assignment map with an empty array of size maxQuota
for all members
Map<String, List<TopicPartition>> assignment = new HashMap<>(
-
consumerToOwnedPartitions.keySet().stream().collect(Collectors.toMap(c -> c, c
-> new ArrayList<>(minQuota))));
+
consumerToOwnedPartitions.keySet().stream().collect(Collectors.toMap(c -> c, c
-> new ArrayList<>(maxQuota))));
+ List<TopicPartition> assignedPartitions = new ArrayList<>();
// Reassign as many previously owned partitions as possible
for (Map.Entry<String, List<TopicPartition>> consumerEntry :
consumerToOwnedPartitions.entrySet()) {
String consumer = consumerEntry.getKey();
List<TopicPartition> ownedPartitions = consumerEntry.getValue();
List<TopicPartition> consumerAssignment = assignment.get(consumer);
- int i = 0;
- // assign the first N partitions up to the max quota, and mark the
remaining as being revoked
- for (TopicPartition tp : ownedPartitions) {
- if (i < maxQuota) {
- consumerAssignment.add(tp);
- unassignedPartitions.remove(tp);
- } else {
- allRevokedPartitions.add(tp);
- }
- ++i;
- }
if (ownedPartitions.size() < minQuota) {
+ // the expected assignment size is more than consumer have
now, so keep all the owned partitions
+ // and put this member into unfilled member list
+ if (ownedPartitions.size() > 0) {
+ consumerAssignment.addAll(ownedPartitions);
+ assignedPartitions.addAll(ownedPartitions);
+ }
unfilledMembers.add(consumer);
+ } else if (ownedPartitions.size() >= maxQuota &&
numMembersHavingMorePartitions < expectedNumMembersHavingMorePartitions) {
+ // consumer owned the "maxQuota" of partitions or more, and
we're still under the number of expected max capacity members
+ // so keep "maxQuota" of the owned partitions, and revoke the
rest of the partitions
+ numMembersHavingMorePartitions++;
+ List<TopicPartition> maxQuotaPartitions =
ownedPartitions.subList(0, maxQuota);
+ consumerAssignment.addAll(maxQuotaPartitions);
+ assignedPartitions.addAll(maxQuotaPartitions);
+ allRevokedPartitions.addAll(ownedPartitions.subList(maxQuota,
ownedPartitions.size()));
} else {
- // It's possible for a consumer to be at both min and max
capacity if minQuota == maxQuota
- if (consumerAssignment.size() == minQuota)
- minCapacityMembers.add(consumer);
- if (consumerAssignment.size() == maxQuota)
- maxCapacityMembers.add(consumer);
+ // consumer owned at least "minQuota" of partitions
+ // so keep "minQuota" of the owned partitions, and revoke the
rest of the partitions
+ List<TopicPartition> minQuotaPartitions =
ownedPartitions.subList(0, minQuota);
+ consumerAssignment.addAll(minQuotaPartitions);
+ assignedPartitions.addAll(minQuotaPartitions);
+ allRevokedPartitions.addAll(ownedPartitions.subList(minQuota,
ownedPartitions.size()));
+ // this consumer is potential maxQuota candidate since we're
still under the number of expected max capacity members
+ if (numMembersHavingMorePartitions <
expectedNumMembersHavingMorePartitions) {
+ unfilledMembers.add(consumer);
+ }
}
}
+ List<TopicPartition> unassignedPartitions =
getUnassignedPartitions(totalPartitionsCount, partitionsPerTopic,
assignedPartitions);
+ assignedPartitions = null;
+
+ if (log.isDebugEnabled()) {
+ log.debug("After reassigning previously owned partitions, unfilled
members: {}, unassigned partitions: {}, " +
+ "current assignment: {}", unfilledMembers,
unassignedPartitions, assignment);
+ }
+
Collections.sort(unfilledMembers);
- Iterator<TopicPartition> unassignedPartitionsIter =
unassignedPartitions.iterator();
-
- // Fill remaining members up to minQuota
- while (!unfilledMembers.isEmpty() && !unassignedPartitions.isEmpty()) {
- Iterator<String> unfilledConsumerIter = unfilledMembers.iterator();
-
- while (unfilledConsumerIter.hasNext()) {
- String consumer = unfilledConsumerIter.next();
- List<TopicPartition> consumerAssignment =
assignment.get(consumer);
-
- if (unassignedPartitionsIter.hasNext()) {
- TopicPartition tp = unassignedPartitionsIter.next();
- consumerAssignment.add(tp);
- unassignedPartitionsIter.remove();
- // We already assigned all possible ownedPartitions, so we
know this must be newly to this consumer
- if (allRevokedPartitions.contains(tp))
- partitionsTransferringOwnership.put(tp, consumer);
- } else {
- break;
- }
- if (consumerAssignment.size() == minQuota) {
- minCapacityMembers.add(consumer);
- unfilledConsumerIter.remove();
+ Iterator<String> unfilledConsumerIter = unfilledMembers.iterator();
+ // Round-Robin filling remaining members up to the expected numbers of
maxQuota, otherwise, to minQuota
+ for (TopicPartition unassignedPartition : unassignedPartitions) {
+ if (!unfilledConsumerIter.hasNext()) {
+ if (unfilledMembers.isEmpty()) {
+ // Should not enter here since we have calculated the
exact number to assign to each consumer
+ // There might be issues in the assigning algorithm, or
maybe assigning the same partition to two owners.
Review comment:
nit (for next PR): can you log an error before throwing the exception
and include the set of unassigned partitions? Either just print out the
`unassignedPartitions` along with the current partition being processed so you
can figure out which partitions are remaining after that, or else by actually
computing the remaining partitions that have yet to be assigned. Since it's an
error case, I think it's ok to spend a little extra time computing that for
better debuggability
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