1.
Consumer offset management
in Kafka
Joel Koshy
Kafka meetup @ LinkedIn
March 24, 2015

2.
Consumers and offsets
5 6 7 8 9
1
0
1
1
1
2
1
3
1
4
1
5
1
6
2
3
2
4
2
5
2
6
2
7
2
8
2
9
3
0
3
1
3
2
3
3
3
4
PageViewEvent-0
EmailBounceEvent-0
PageViewEvent-0
EmailBounceEvent-0 35
12
Offset map
GroupId: audit-consumer

3.
Store offsets in ZooKeeper
admin
brokers
config
consumers
controller
controller_epoch
audit-consumer
ids
owners
offsets
PageViewEvent
EmailBounceEvent
0
0
12
35

4.
(Don’t) store offsets in ZooKeeper
• Heavy write-load on ZooKeeper
• Especially an issue
– during 0.7 to 0.8 migration
– and before we switched to SSDs
• Non-ideal work-arounds
– Increase offset-commit intervals
– Filter commits if offsets have not moved
– Spread large offset commits over commit
interval

5.
Offset management (ideals)
• Durable
• Support high write-load
• Consistent reads
• Atomic offset commits
• Fast commits/fetches

6.
Store offsets in a replicated log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets Next commit
Group
Offset
Partition

7.
Store offsets in a replicated log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets
audit-consumer
EmailBounceEvent-0
248

8.
Store offsets in a replicated log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323

9.
Store offsets in a replicated log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323
mirrormaker
ClickEvent-0
54543

10.
Store offsets in a
replicated, partitioned log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets, partition 3
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323
mirrormaker
ClickEvent-0
54543
mirrormaker
ClickEvent-1
54444
mirrormaker
ClickEvent-1
54674
__consumer_offsets, partition 8
Partition è abs(GroupId.hashCode()) % NumPartitions

11.
Store offsets in a
replicated, partitioned log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets, partition 3
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323
mirrormaker
ClickEvent-0
54543
mirrormaker
ClickEvent-1
54444
mirrormaker
ClickEvent-1
54674
__consumer_offsets, partition 8
Offset commits append to the offsets topic partition
Offset fetches read from the offsets topic partition

12.
Store offsets in a
replicated, partitioned log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets, partition 3
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323
mirrormaker
ClickEvent-0
54543
mirrormaker
ClickEvent-1
54444
mirrormaker
ClickEvent-1
54674
__consumer_offsets, partition 8
[audit-consumer, PageViewEvent-0]
[audit-consumer, EmailBounceEvent-0]
[mirrormaker, ClickEvent-0]
[mirrormaker, ClickEvent-1]
Offsets cache
323
248
54674
54543
Offset commits append to the offsets topic partition + update the cache
Offset fetches read from the offsets topic partition cache

13.
Store offsets in a
replicated, partitioned log
audit-consumer
PageViewEvent-0
240
audit-consumer
EmailBounceEvent-0
232
__consumer_offsets, partition 3
audit-consumer
EmailBounceEvent-0
248
audit-consumer
PageViewEvent-0
323
mirrormaker
ClickEvent-0
54543
mirrormaker
ClickEvent-1
54444
mirrormaker
ClickEvent-1
54674
__consumer_offsets, partition 8
[audit-consumer, PageViewEvent-0]
[audit-consumer, EmailBounceEvent-0]
[mirrormaker, ClickEvent-0]
[mirrormaker, ClickEvent-1]
Offsets cache
323
248
54674
54543
Offset commits append to the offsets topic partition + update the cache
Offset fetches read from the offsets topic partition cache
How do we GC older offset entries?

14.
log.cleanup.policy = compact
0 1 2 3 4 5 6 7 8 9 10
K1 K2 K1 K1 K3 K2 K4 K5 K5 K2 K6
V1 V2 V3 V4 V5 V6 V7 V8 V9
V
10
V
11
3 4
K1 K3
V4 V5
6
K4
V7
8 10
K5 K6
V9
V
11
Compaction
Offset
Key
Value
11
K2
Ø
Offset
Key
Value

15.
Store offsets in a
replicated, partitioned, compacted
log
audit-consumer
PageViewEvent-0
126312342
audit-consumer
EmailBounceEvent-0
59843
audit-consumer
PageViewEvent-0
126319628
audit-consumer
EmailBounceEvent-0
86243
audit-consumer
PageViewEvent-0
126398102
Key
Value
audit-consumer
EmailBounceEvent-0
86243
audit-consumer
PageViewEvent-0
126398102
Compaction
Key è [Group, Topic, Partition]
Value è Offset

16.
Dealing with dead consumers
console-consumer-38587, console-consumer-94777, console-consumer-94774, console-consumer-31199,
console-consumer-51555, console-consumer-43182, mobileServiceConsumerDwwewewA13dafddesfasdfdee33,
console-consumer-57784, python-kafka-consumer-0959a04da7c241448beb0813f002e34b, console-
consumer-70750, console-consumer-94809, console-consumer-87470, touch-me-not, console-
consumer-43246, console-consumer-69811, python-kafka-consumer-82c2d653128840d5b6bcbfc5ac7f3abc,
console-consumer-33847, console-consumer-18217, console-consumer-87493, console-consumer-26414,
console-consumer-67299, voldemort-reader-jjkoshy, console-consumer-80245,
kafka_listener_for_comments, test-flow-staging, console-consumer-8441, console-consumer-67258, data-
processor-2, console-consumer-94869, console-consumer-55242, pinot-beta-hackday_1_2, console-
consumer-6601, cloud-host1, system-metrics-monitor-01, console-consumer-70859, console-
consumer-26477, page-view-test-flow-2, page-view-test-flow-1, python-kafka-consumer-
bf33d075b22d4ddfb82d4a055303e909, console-consumer-99768, console-consumer-45509, console-
consumer-21504, points-test_devel_l1_1686489164, console-consumer-14841, console-consumer-4098,
console-consumer-14746, console-consumer-94575, cloud-dcb-host147.company.com,
teacup_reporting_alex, console-consumer-4132, console-consumer-48171, ropod-dcb-host794.company.com,
console-consumer-63743, console-consumer-36147, console-consumer-48138, console-consumer-33595,
console-consumer-6808, console-consumer-31000, console-consumer- 73064, console-consumer-18050,
console-consumer-21683, share-message, ropod-dcb-host959.company.com, ropod-dcb-host949.company.com,
sensei-test_dcb_host138.company.com_1924844804, console-consumer-38654, console-consumer-92040,
console-consumer-67052, console-consumer-82690, console-consumer-92002, console-consumer-69687,
console-consumer-31077, console-consumer-94657, console-consumer-36064, console-consumer-45675,
console-consumer-45671, console-consumer-70625, MemberSettings-dcx, console-consumer-55513, member-
links-dcx, console-consumer-85367, opportunist-company, forum-queue, console-consumer-87912,
console-consumer-75909, console-consumer-12320, sensei-test_user2_808173709, ropod-dcb-
host937.company.com, console-consumer-8710, console-consumer-48390, python-kafka-
consumer-816cebafabb34dd5be6bfce59cbee411, console-consumer-8701, console-consumer-6122, console-
consumer-6142, metrics-dcb-monitor19, console-consumer-73329, console-consumer-87942, console-
consumer-80552, console-consumer-48368, autometrics-dcb-host13, …!

17.
Dealing with dead consumers
• For offsets older than offset retention
period:
– Append tombstone
– Remove offset entry from cache

18.
Recommended settings for
offsets topic
Replication factor >= 3
min.insync.replicas >= 2
unclean.leader.election.enable False
offsets.commit.required.acks -1 (all)

19.
How to commit/fetch offsets
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
__consumer_offsets-34: Leader: 2, ISR: 0, 1, 2
V
I
P
Consumer
metadata
request
Response
(manager=2)

20.
How to commit/fetch offsets
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
__consumer_offsets-34: Leader: 2, ISR: 0, 1, 2
Offset
fetches
Offset
commits
cache
replication

21.
When the offset manager moves
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
__consumer_offsets-34: Leader: 2, ISR: 0, 1, 2
cache
Become
Leader
load
cache

22.
When the offset manager moves
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
__consumer_offsets-34: Leader: 2, ISR: 0, 1, 2
cache
Become
Leader
load
cache
Become
follower
XXXXXX

23.
When the offset manager moves
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
Offset
fetches
Offset
commits
cache
__consumer_offsets-34: Leader: 0, ISR: 0, 1, 2
cache
X
X

24.
When the offset manager moves
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
V
I
P
Consumer
metadata
request
cache
__consumer_offsets-34: Leader: 0, ISR: 0, 1, 2
cache
Response
(manager=0)

25.
When the offset manager moves
audit-consumer
Consumer
instance
Broker 0
Broker 1
Broker 2
Broker 3
(controller)
cache
__consumer_offsets-34: Leader: 0, ISR: 0, 1, 2
cache
Offset
commits
Offset
fetches
replication

26.
Offset{Commit,Fetch} API
ConsumerMetadataRequest
o Group Id: String
ConsumerMetadataResponse
o Error code: Short
o Offset manager: Kafka broker info

27.
Offset{Commit,Fetch} API
OffsetCommitRequest
o groupId: String
o Offset map
§ Key è Topic-partition
§ Value è Partition-data
• Offset: Long
• Timestamp: Long
• Metadata: String
KAFKA-1634: changes semantics of timestamp
to retention

28.
Offset{Commit,Fetch} API
OffsetCommitResponse
o Response map
§ Key è Topic-partition
§ Value è Error code

29.
Offset{Commit,Fetch} API
OffsetFetchRequest
o Group Id: String
o Partitions: List<Topic-partition>
OffsetFetchResponse
o Response map
§ Key è Topic-partition
§ Value è Partition-data
• Offset: Long
• Metadata: String
• Error code: Short

30.
Offset{Commit,Fetch} API
Code samples: http://bit.ly/1LTJBYo

31.
Offset{Commit,Fetch} API
KafkaConsumer<K, V> consumer = new KafkaConsumer<K, V>(properties);!
…!
TopicPartition partition1 = new TopicPartition("topic1", 0);!
TopicPartition partition1 = new TopicPartition("topic1", 1);!
!
consumer.subscribe(partition1, partition2);!
!
Map<TopicPartition, Long> offsets = new LinkedHashMap<TopicPartition,
Long>();!
offsets.put(partition1, 123L);!
offsets.put(partition2, 4320L);!
…!
// commit offsets!
consumer.commit(offsets, CommitType.SYNC);!
…!
// fetch offsets!
long committedOffset = consumer.committed(partition1);!
!

32.
How to read the offsets topic
To read everything, use the console consumer!
./bin/kafka-console-consumer.sh --topic __consumer_offsets --
zookeeper localhost:2181 --formatter "kafka.server.OffsetManager
$OffsetsMessageFormatter" --consumer.config config/
consumer.properties!
(Must set exclude.internal.topics = false in consumer.properties)
!
To read a single partition, use the simple-
consumer-shell
./bin/kafka-simple-consumer-shell.sh --topic __consumer_offsets --
partition 12 --broker-list localhost:9092 --formatter
"kafka.server.OffsetManager$OffsetsMessageFormatter"!

33.
Inside the offsets topic
[Group, Topic, Partition]::[Offset, Metadata, Timestamp]
[audit-consumer,PageViewEvent,7]::OffsetAndMetadata[53568,NO_METADATA,1416363620711]!
[audit-consumer,service-log-event,5]::OffsetAndMetadata[168012,NO_METADATA,
1416363620711]!
[audit-consumer,EmailBounceEvent,4]::OffsetAndMetadata[8524676,NO_METADATA,
1416363620711]!
[audit-consumer,ClickEvent,0]::OffsetAndMetadata[8132292,NO_METADATA,1416363620711]!
[audit-consumer,metrics-event,1]::OffsetAndMetadata[1835900,NO_METADATA,1416363620711]!
[audit-consumer,CompanyEvent,0]::OffsetAndMetadata[109337,NO_METADATA,1416363620711]!
[audit-consumer,test-topic,1]::OffsetAndMetadata[352989,NO_METADATA,1416363620711]!
[audit-consumer,meetup-event,2]::OffsetAndMetadata[39961,NO_METADATA,1416363620711]!
[audit-consumer,push-topic,6]::OffsetAndMetadata[4210366,NO_METADATA,1416363620711]!

34.
How to migrate/roll-back
Migrate from ZooKeeper to Kafka:
• Config change
– offsets.storage=kafka
– dual.commit.enabled=true
• Rolling bounce
• Config change
– dual.commit.enabled=false
• Rolling bounce

35.
How to migrate/roll-back
Migrate from Kafka to ZooKeeper:
• Config change
– dual.commit.enabled=true
• Rolling bounce
• Config change
– offsets.storage=zookeeper
– dual.commit.enabled=false
• Rolling bounce

36.
Key metrics to monitor
• Consumer mbeans
– Kafka commit rate
– ZooKeeper commit rate (during migration)
• Broker mbeans
– Max-dirty ratio and other log cleaner metrics
– Offset cache size
– Group count
– {ConsumerMetadata, OffsetCommit, OffsetFetch}
request metrics

37.
0.8.3
• Support compression in compacted topics
(KAFKA-1734)
• Change offset commit “timestamp” to
mean retention period: KAFKA-1634
• Offset client

38.
Monitor it!

39.
Acknowledgments
Kafka team @ LinkedIn
Jay Kreps, Jun Rao, Neha Narkhede @ Confluent
Tejas (2013 intern): http://lnkdin.me/p/tejaspatil1