Producer Performance Tuning for Apache Kafka

Producer Performance Tuning
For Apache Kafka
Jiangjie (Becket) Qin @ LinkedIn
Streams Meetup @ LinkedIn
June 15, 2015

What is Apache Kafka?
“ Kafka is a high throughput low latency ….. ”
Performance tuning is
● still very important!
● a case by case process based on
○ Different data pattern
○ Performance objectives
2

Agenda
● The goal of producer performance tuning
● Understand Kafka Producer
● Producer performance tuning
○ ProducerPerformance tool
○ Quantitative analysis using producer metrics
○ Play with a toy example
● Some real world examples
○ Latency when acks=-1
○ Produce when RTT is long
● Q & A
3

Agenda
● Understand Kafka Producer
● Q & A
4

The goal of producer performance tuning
With a given dataset to send:
● Achieve the throughput and latency goals with guarantees of
○ Durability
○ Ordering
● Focus on the average producer performance
○ 99 percentile performance sometimes cannot be “tuned”
○ Tuning average performance also helps 99 percentile numbers
● Today’s talk
○ Fixed data pattern (1000 bytes of integers ranging between 0 - 50000)
5

Agenda
● Understand the Kafka Producer
● Q & A
6

Understand the Kafka producer
● org.apache.kafka.producer.KafkaProducer
○ If you are still using OLD producer, please upgrade!
● Benchmarks in this talk use Kafka 0.10.0
○ No broker side recompression (KIP-31)
○ 8 bytes overhead per message due to the introduction of timestamp (KIP-32)
7

Critical Configurations
● batch.size
● linger.ms
● compression.type
● max.in.flight.requests.per.connection (affects ordering)
● acks (affects durability)
8

User: producer.send(new ProducerRecord(“topic0”, “hello”), callback);
● Serialization
9
topic=“topic0”
value=“hello”
Serializer

Topic
Metadata
topic=“topic0”
value=“hello”
PartitionerSerializer
● Serialization
● Partitioning
topic=“topic0”
partition =0
value=“hello”
10

Record Accumulator
batch0 batch1 topic0, 0● Serialization
● Partitioning
Topic
Metadata
topic=“topic0”
value=“hello”
topic=“topic0”
partition =0
value=“hello”
11

Record Accumulator
● Partitioning
freeused
compressor
callbacks
Topic
Metadata
topic=“topic0”
value=“hello”
topic=“topic0”
partition =0
value=“hello”
12

Record Accumulator
● Partitioning
● Compression
freeused
compressor
callbacks
MTopic
Metadata
topic=“topic0”
value=“hello”
topic=“topic0”
partition =0
value=“hello”
13

Record Accumulator
● Partitioning
● Compression
Tasks done by the user threads.
freeused
compressor
callbacks
M
CB
Topic
Metadata
topic=“topic0”
value=“hello”
topic=“topic0”
partition =0
value=“hello”
14

Record Accumulator
…...
batch0 batch1
batch0
batch0 batch1
topic0, 0
topic0, 1
topic1, 0batch2
freeused
compressor
callbacks
M
CB
sender thread
15
Sender:
1. polls batches from the batch queues (one batch / partition)

Sender:
2. groups batches based on the leader broker
Record Accumulator
…...
batch1
batch1
topic0, 0
topic0, 1
topicN, Mbatch2
sender thread
batch0
batch0
batch0
request 0
request 1
Broker 0
Broker 1
(one batch / partition)
freeused
compressor
callbacks
M
CB
16

Sender:
3. sends the grouped batches to the brokers
4. Pipelining if max.in.flight.requests.per.connection > 1
Record Accumulator
…...
batch1
batch1
topic0, 0
topic0, 1
topicN, Mbatch2
sender thread
batch0
batch0
batch0
request 0
request 1
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
17

Sender:
3. sends the grouped batches to the brokers
4. Pipelining if max.in.flight.requests.per.connection > 1
Record Accumulator
…...
batch1
batch1
topic0, 0
topic0, 1
topicN, Mbatch2
sender thread
batch0
batch0
batch0
request 0
request 1
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
18
resp
resp

sender thread
Sender:
A batch is ready when one of the following is true:
● batch.size is reached
● linger.ms is reached
● Another batch to the same broker is ready (piggyback)
● flush() or close() is called
Record Accumulator
…...
batch1
batch1
topic0, 0
topic0, 1
topicN, Mbatch2
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
19

sender thread
Record Accumulator
…...
topic0, 0
topic0, 1
topicN, Mbatch2
batch1 batch1
request 2
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
20
Sender:

sender thread
Record Accumulator
…...
topic0, 0
topic0, 1
topicN, Mbatch2
batch1 batch1
request 2
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
21
Sender:

sender thread
Record Accumulator
…...
topic0, 0
topic0, 1
topicN, Mbatch2
batch1 batch1
request 2
Broker 0
Broker 1
freeused
compressor
callbacks
M
CB
callbacks CB
resp
22
Sender:
On receiving the response
● The callbacks are fired in the message sending order

batch.size & linger.ms
batch.size is size based batching
linger.ms is time based batching
In general, more batching
● ⇒ Better compression ratio ⇒ Higher throughput
● ⇒ Higher latency
23

compression.type
● Compression is usually the dominant part of the producer.send()
● The speed of different compression types differs A LOT
● Compression is in user thread, so adding more user threads helps with
throughput if compression is slow
24

acks
Defines different durability level for producing.
acks Throughput Latency Durability
0 high low No guarantee
1 medium medium leader
-1 low high ISR
25

max.in.flight.requests.per.connection
max.in.flight.requests.per.connection > 1 means pipelining.
In general, pipelining
● gives better throughput
● may cause out of order delivery when retry occurs
● Excessive pipelining ⇒ Drop of throughput
○ lock contention
○ worse batching
We will be using max.in.flight.requests.per.connection=1 for today’s
talk.
26

Agenda
● Understand KafkaProducer
● Q & A
27

ProducerPerformance Tool
Useful producer performance tuning tool:
● org.apache.kafka.tools.ProducerPerformance
Example:
./kafka-producer-perf-test.sh --num-records 1000000 --record-size 1000 --topic
becket_test_3_replicas_1_partition --throughput 1000000 --producer-props bootstrap.
servers=localhost:9092 max.in.flight.requests.per.connection=1 batch.size=100000
compression.type=lz4
28

ProducerPerformance Tool
Useful producer performance tuning tool:
● org.apache.kafka.tools.ProducerPerformance
With KAFKA-3554:
becket_test_3_replicas_1_partition --throughput 1000000 --num-threads 2 --value-bound 50000
--producer-props bootstrap.servers=localhost:9092 max.in.flight.requests.per.connection=1
batch.size=100000 compression.type=lz4
● --num-threads : The number of the user threads to send messages.
● --value-bound : The range of the random integer in the messages. This option is useful when compression is used.
Different integer range simulates different compression ratio.
29

Quantitative analysis using producer metrics
The improved ProducerPerformance tool (KAFKA-3554) prints the following
producer metrics.
● Select_Rate_Avg (The rate that the sender thread runs to check if it can send some messages)
● Request_Rate_Avg
● Request_Latency_Avg (Not including the callback execution time)
● Request_Size_Avg (After compression)
● Batch_Size_Avg (After compression)
● Records_Per_Request_Avg
● Record_Queue_Time_Avg
● Compression_Rate_Avg
Note: The metrics need some time (~ 1 min) to become stable.
30

becket_test_3_replicas_4_partition --throughput 100000 --num-threads 1 --value-bound 50000
--producer-props bootstrap.servers=localhost:9092 compression.type=gzip max.in.flight.
requests.per.connection=1
1000000 records sent, 10444.300545 records/sec (9.96 MB/sec), 4.19 ms avg latency, 154.00 ms max latency, 4 ms 50th,
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
Select_Rate_Avg: 3114.67
Request_Rate_Avg: 1448.53
Request_Latency_Avg: 2.73
Request_Size_Avg: 5034.47
Batch_Size_Avg: 4941.93
Records_Per_Request_Avg: 7.05
Record_Queue_Time_Avg: 2.45
Compression_Rate_Avg: 0.68
31

1. throughput_Avg ~= Request_Rate_Avg * Request_Size_Avg / Compression_Rate_Avg
./kafka-producer-perf-test.sh --num-records 1000000 --record-size 1000 --topic becket_test_3_replicas_4_partition --
throughput 100000 --num-threads 1 --value-bound 50000 --producer-props bootstrap.servers=localhost:9092 compression.
type=gzip max.in.flight.requests.per.connection=1
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
1448.53 * 5034.47 / 0.68 = 10.22 MB/sec
(The gap is due to the request_overhead)
32

2. Request_Size_Avg = Records_Per_Request_Avg * Record_Size * Compression_Rate_Avg +
Request_Overhead
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
7.05 * 1000 * 0.68 + Request_Overhead = 4794 + Request_Overhead
The Request_Overhead:
● depends on the number of topics and partitions
● usually ranges from dozens bytes to hundreds of bytes.
33

3. Request_Rate_Upper_Limit = (1000 / Request_Latency_Avg) * Num_Brokers
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
(1000 / 2.73) * 5 = 1813
The gap is:
● due to the producer overhead,
● larger if request rate is higher
34

4. latency_avg ~= (Record_Queue_Time_Avg / 2) + Request_Latency_Avg + Callback_Latency
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
2.45 / 2 + 2.73 + Callback_Latency = 3.96 + Callback_Latency
(The callback latency and some other time cost in the
ProducerPerformance tool is usually small enough to ignore)
35

Play with a toy example
6 ms 95th, 6 ms 99th, 22 ms 99.9th.
● RTT=1.55 ms
● 5 broker cluster
36

6 ms 95th, 6 ms 99th, 22 ms 99.9th.
● Network Bandwidth = 1 Gbps:
○ Throughput can be improved
37

6 ms 95th, 6 ms 99th, 22 ms 99.9th.
throughput_Avg ~= Request_Rate_Avg * Request_Size_Avg / Compression_Rate_Avg
● RTT = 1.55 ms:
○ Request Latency is not bad.
● 1448 Request rate is not bad
○ 5 brokers * (1000 / 2.73) = 1813 (theoretical upper limit)
● Each request is too small
○ Default batch size = 16KB
38

6 ms 95th, 6 ms 99th, 22 ms 99.9th.
Ways to increase request size:
1. Add more user threads
2. Increase number of partitions
3. Increase linger.ms (more batching)
39

6 ms 95th, 6 ms 99th, 22 ms 99.9th.
Ways to increase request size:
1. Add more user threads
2. Increase number of partitions
3. Increase linger.ms (more batching)?
40

More Batching
41
More batching does not help!?

More Batching
42
Compression Ratio is not improved much!

More Batching
43
Compression Ratio is not improved much!
But why throughput becomes worse!?

Impact of Batch Size on GZIP Compression
44
When batch size is doubled from 16K to 32K, the time needed to fill in the batch is
almost tripled!
(The results are from JMH Micro Benchmark)
batch size (KB)
Time to fill up the
batch (ns)
16 1768583.939
32 5234432.44
64 13307411.93
128 29539258.9
192 45549678.03
256 61579312.57

45
Batch_Size_Avg: Record_Queue_Time_Avg:
15075.84 3.86
30681.25 9.37
61687.88 21.12
124451.51 47.2
248860.43 92.14
498640.58 184.84
When batch size is doubled from 16K to 32K, the time needed to fill in the batch is
2.5x!
(The results are from ProducerPerformance tool with 1 user thread, 1 partition,
linger.ms=20000)

46
Different value bounds show similar results.

Impact of Batch Size on Compression
47
Snappy and LZ4 has similar impact at different batch size.

When to increase batching
● Compression Ratio Gain > Compression Speed Loss
● Bottleneck is not in the user threads
48

OK… Let’s increase number of user threads then.
49
When there are 10 user threads:
● Throughput drops
● Latency soars

OK… Let’s increase number of user threads then.
50
● Lock contention (10 user threads V.S. 4 partitions)
● batches are piling up!
When there are 10 user threads:
● Throughput drops
● Latency soars
Records Queue Time = 3323.85 ms

When topic has 16 partitions
51
Batches are still piling up, but it
seems much better than before.
Records Queue Time = 252.69 ms

Let’s try tweak the batch size.
--num-threads 10, batch.size=16K, 16 partitions
2000000 records sent, 39791.492579 records/sec (37.95 MB/sec), 152.77 ms avg latency, 1182.00 ms max latency, 14 ms
50th, 841 ms 95th, 1128 ms 99th, 1162 ms 99.9th.
(Requests are piling up, so the bottleneck is the sender thread)
--num-threads 10, batch.size=800K, 16 partitions
50th, 37 ms 95th, 68 ms 99th, 325 ms 99.9th.
(Requests are no longer piling up, the bottleneck shifted to user threads)
Usually bigger batch leads to bigger latency.
But increasing batch size can improve latency by preventing the batches from piling up!
52

To improve both latency & throughput? Increase number of partitions again.
--num-threads 10, batch.size=16K
50th, 841 ms 95th, 1128 ms 99th, 1162 ms 99.9th.
--num-threads 10, batch.size=800K
50th, 37 ms 95th, 68 ms 99th, 325 ms 99.9th.
--num-threads 10, batch.size=16K, 32 partitions.
50th, 225 ms 95th, 246 ms 99th, 270 ms 99.9th.
53

Find the throughput bottleneck
Is the bottleneck in user thread?
● Increase --num-threads and see if throughput increases accordingly
● Pay attention to lock contention
Is the bottleneck in sender thread?
● Is throughput (MB/sec) << network bandwidth
● Is Record_Queue_Time_Avg large?
● Is Batch_Size_Avg almost equals to batch.size?
Is the bottleneck in broker?
● Is the request latency very large?
54

Agenda
● Q & A
55

Latency when acks=-1
Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
Partition 0
Partition 1
Partition 2
1
2
Producer 3
4
ProduceResponse
5
1. [Network] ProduceRequest Send Time
2. [Broker] ProduceRequest Queue Time
3. [Broker] ProduceRequest Local Time
4. [Broker] ProduceRequest Remote Time
5. [Broker] ProduceResponse Queue Time
6. [Broker] ProduceResponse Send Time
6
56

Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
Partition 0
Partition 1
Partition 2
1
2
Producer 3
4
ProduceResponse
5
1. [Network] ProduceRequest Send Time
2. [Broker] ProduceRequest Queue Time
3. [Broker] ProduceRequest Local Time
4. [Broker] ProduceRequest Remote Time (Replication Time)
5. [Broker] ProduceResponse Queue Time
6. [Broker] ProduceResponse Send Time
6
57

Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
high watermark fetch (p0,100; p1,200; p2,50)
100 105
● The followers fetches data of the partitions from the leader.
● The leader uses high watermarks to the In Sync Replicas
(ISR) of the all partitions
58
200
50
200
50
Partition 0
Partition 1
Partition 2
100

Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
Partition 0
Partition 1
Partition 2
p0
high watermark
100 105
p0
The high watermarks are not updated after the data is sent.
100
fetch (p0,100; p1,200; p2,50)
59
200
50
200
50

Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
Partition 0
Partition 1
Partition 2
p0
high watermark
100 105
p0
p0
100 105
fetch (p0,100; p1,200; p2,50)
60
200
50
200
50

Broker 0 Broker 1
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
Partition 0
Partition 1
Partition 2
p0
high watermark
100 105
p0
p0
100 105
fetch (p0,100; p1,200; p2,50)
61
200
50
200
50
p1
p2
203
60

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
The high watermark increases lazily. There is one fetch delay.
100 105
fetch (p0,100; p1,200; p2,50)
200
50
200
50
62
p1
p2
203
60
high watermark

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
The high watermark increases lazily. There is one fetch delay.
100 105
fetch (p0,100; p1,200; p2,50)
200
50
200
50
63
p1
p2
203
60
high watermark

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
ProduceResponse
p1 p1
p2 p2
The replication is not ProduceRequest aware.
● The messages produced in the same ProduceRequest may
be replicated in multiple fetches.
● ProduceRequests interfere with each other.
100 105
p1 p2
fetch (p0,100; p1,200; p2,50)
200 203
50 60
200 203
50 60
64
high watermark

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
ProduceResponse
p1 p1
p2 p2
Only when the high watermarks of all the partitions has passed the
offset of the appended messages in the ProduceRequest, the
ProduceResponse will be sent.
100 105
p1 p2
fetch (p0,100; p1,200; p2,50)
fetch (p0,105; p1,203; p2,60)
200 203
50 60
200 203
50 60
65
high watermark

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
ProduceResponse
p1 p1
p2 p2
Only when the high watermarks of all the partitions has passed the
offset of the appended messages in the ProduceRequest, the
ProduceResponse will be sent.
100 105
p1 p2
fetch (p0,100; p1,200; p2,50)
fetch (p0,105; p1,203; p2,60)
200 203
50 60
200 203
50 60
66
high watermark

fetch (p0,105; p1,200; p2,50)
Broker 0
Partition 0
Partition 1
Partition 2
p0 p1 p2
ProduceRequest
p0
100 105
p0
Broker 1
Partition 0
Partition 1
Partition 2
p0
ProduceResponse
p1 p1
p2 p2
Assuming broker 1 only has one replication thread,
Replication Time ~= Num_Fetches * (Local_Time_On_The_Follower +
Fetch_Request_Total_Time_On_The_Leader)
100 105
p1 p2
fetch (p0,100; p1,200; p2,50)
fetch (p0,105; p1,203; p2,60)
200 203
50 60
200 203
50 60
67
high watermark

Replication Time ~= Num_Fetches * (Local_Time_On_The_Follower +
Fetch_Request_Total_Time_On_The_Leader)
/ num.replica.fetchers
● Increase num.replica.fetchers
○ Parallel fetch
○ Each replica fetcher fetches from a distinct set of partitions.
● Not perfect solution
○ Diminishing effect
○ Scalability concern
■ Replica fetchers per broker = (Cluster_Size - 1 ) * num.replica.fetchers
68

How many replica fetchers are enough?
● The latency target is met
● If Replica FetchRequest Remote Time > 0
○ The replica fetch requests are waiting for the messages to arrive.
○ Increasing num.replica.fetchers won’t improve latency.
● Partitions per replica fetcher is low
69

Agenda
● Q & A
70

Produce when RTT is long
We have a cross-ocean pipeline using remote produce
● RTT is big (~200 ms)
● Bandwidth = 1 Gb/s
● Batch size 800K
● Linger.ms 30ms
● 64 Partitions
● 8 user threads
71

We have a cross-ocean pipeline using remote produce
● RTT is big (~200 ms)
● Bandwidth = 1 Gb/s
● Batch size 800K
● Linger.ms 30ms
● 64 Partitions
● 8 user threads
● Throughput < 1 MB/s
72

The TCP connection needs more send and receive buffer.
Broker default: socket.receive.buffer.bytes = 100K
Producer default: send.buffer.bytes = 128K
Theoretical throughput with default setting = 100K / RTT = 500KB
Theoretical best buffer size = RTT * Bandwidth = 0.2s * 1 Gb/s = 25 MB
73

Changing socket buffer size may require OS TCP buffer limit.
74

Changing socket buffer size may require OS TCP buffer limit.
# The default setting of the socket receive buffer in bytes.
net.core.rmem_default = 124928
# The maximum receive socket buffer size in bytes.
net.core.rmem_max = 2048000
# The default setting (in bytes) of the socket send buffer.
net.core.wmem_default = 124928
# The maximum send socket buffer size in bytes.
net.core.wmem_max = 2048000
75

Q&A
76
Backup slides are following.

Producer Metrics With 4 Partitions
77
1 thread 2 threads 4 threads 10 threads
Select_Rate_Avg: 3114.67 682.55 1359.05 2641.75
Request_Rate_Avg: 1448.53 1282.76 840.36 634.22
Request_Latency_Avg: 2.73 3.11 4.62 6.09
Request_Size_Avg: 5034.47 8703.1 13192.99 14931.51
Batch_Size_Avg: 4941.93 8607.87 13098.74 14837.54
Records_Per_Request_Avg: 7.05 12.46 19.08 21.63
Record_Queue_Time_Avg: 2.45 2.79 5.17 3323.85
Compression_Rate_Avg: 0.68 0.67 0.66 0.66

Producer Metrics With 16 Partitions
78
1 Thread 2 Threads 4 Threads 10 Threads
Select_Rate_Avg: 2746.74 1948.27 1241.82 2199.14
Request_Rate_Avg: 1270.49 1093.21 812.54 568.09
Request_Latency_Avg: 3.91 4.53 6.07 8.16
Request_Size_Avg: 8758.02 15447.04 27688.3 45652.14
Batch_Size_Avg: 2706.87 4808.15 8638.38 14283.30
Records_Per_Request_Avg: 12.01 21.82 39.86 66.33
Record_Queue_Time_Avg: 3.13 3.86 6.42 252.69
Compression_Rate_Avg: 0.68 0.67 0.66 0.66

Lock contention for sender thread
Threads 2 4 8 10
linger.ms 50 30 20 15
Record_Queue_Time_Avg 50 31.08 21.21 17.27
Difference 0 1.08 1.21 2.27
This table shows some evidence of lock contention in the Kafka producer.
For a topic with 16 partitions, we do the following:
● Set linger.ms to make them almost the generating the similar size of batch.
● Compare the difference between linger.ms and Record_Queue_Time_Avg
● The bigger the difference is, the worse the lock contention is between the
sender thread and the user threads.
79

Producer Performance Tuning for Apache Kafka

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