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I have a question regarding retention of topics messages.

I have the following situation:

  • Two Kafka topics;
  • Broker has properties log.retention.hours=1;

Describe command for each of the two topics:

[oracleas@zkafka01vdc bin]$ ./kafka-topics.sh --zookeeper 192.168.163.71:2181 --describe --topic digital-lending
Topic:digital-lending   PartitionCount:3        ReplicationFactor:2     Configs:
        Topic: digital-lending  Partition: 0    Leader: 3       Replicas: 1,3   Isr: 3,1
        Topic: digital-lending  Partition: 1    Leader: 2       Replicas: 2,1   Isr: 1,2
        Topic: digital-lending  Partition: 2    Leader: 3       Replicas: 3,2   Isr: 3,2

[oracleas@zkafka01vdc bin]$ ./kafka-topics.sh --zookeeper 192.168.163.71:2181 --describe --topic digital-onboarding
Topic:digital-onboarding        PartitionCount:1        ReplicationFactor:1     Configs:
        Topic: digital-onboarding       Partition: 0    Leader: 1       Replicas: 1     Isr: 1

The question are:

  1. How is possible that topic digital-onboarding have retention 1 day and digital-lending 1 week (based on my observation - tried several times to take all the messages from queue and for one topics the retention was 1 day and for the other one was 1 week)?

  2. Is there another place where it is setuped besides the --describe command and server.properties file?

Edit 1:

server.properties file:

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# see kafka.server.KafkaConfig for additional details and defaults

############################# Server Basics #############################

# The id of the broker. This must be set to a unique integer for each broker.
broker.id=1

# Switch to enable topic deletion or not, default value is false
delete.topic.enable=true

############################# Socket Server Settings #############################

# The address the socket server listens on. It will get the value returned from
# java.net.InetAddress.getCanonicalHostName() if not configured.
#   FORMAT:
#     listeners = listener_name://host_name:port
#   EXAMPLE:
#     listeners = PLAINTEXT://your.host.name:9092
#listeners=PLAINTEXT://10.206.23.71:9092
listeners=EXTERNAL://zkafka01vdc-pub:9092,INTERNAL://zkafka01vdc-int:9093

# Hostname and port the broker will advertise to producers and consumers. If not set,
# it uses the value for "listeners" if configured.  Otherwise, it will use the value
# returned from java.net.InetAddress.getCanonicalHostName().
#advertised.listeners=PLAINTEXT://zkafka01vdc.bcr.wan:9092
advertised.listeners=EXTERNAL://zkafka01vdc.bcr.wan:9092,INTERNAL://zkafka01vdc-int:9093

# Maps listener names to security protocols, the default is for them to be the same. See the config documentation for more details
#listener.security.protocol.map=PLAINTEXT:PLAINTEXT,SSL:SSL,SASL_PLAINTEXT:SASL_PLAINTEXT,SASL_SSL:SASL_SSL
listener.security.protocol.map=EXTERNAL:PLAINTEXT,INTERNAL:PLAINTEXT

inter.broker.listener.name=INTERNAL

# The number of threads that the server uses for receiving requests from the network and sending responses to the network
num.network.threads=3

# The number of threads that the server uses for processing requests, which may include disk I/O
num.io.threads=8

# The send buffer (SO_SNDBUF) used by the socket server
socket.send.buffer.bytes=102400

# The receive buffer (SO_RCVBUF) used by the socket server
socket.receive.buffer.bytes=102400

# The maximum size of a request that the socket server will accept (protection against OOM)
socket.request.max.bytes=104857600


############################# Log Basics #############################

# A comma seperated list of directories under which to store log files
log.dirs=/zkafka/kafka

# The default number of log partitions per topic. More partitions allow greater
# parallelism for consumption, but this will also result in more files across
# the brokers.
num.partitions=1

# The number of threads per data directory to be used for log recovery at startup and flushing at shutdown.
# This value is recommended to be increased for installations with data dirs located in RAID array.
num.recovery.threads.per.data.dir=1

############################# Internal Topic Settings  #############################
# The replication factor for the group metadata internal topics "__consumer_offsets" and "__transaction_state"
# For anything other than development testing, a value greater than 1 is recommended for to ensure availability such as 3.
offsets.topic.replication.factor=1
transaction.state.log.replication.factor=1
transaction.state.log.min.isr=1

############################# Log Flush Policy #############################

# Messages are immediately written to the filesystem but by default we only fsync() to sync
# the OS cache lazily. The following configurations control the flush of data to disk.
# There are a few important trade-offs here:
#    1. Durability: Unflushed data may be lost if you are not using replication.
#    2. Latency: Very large flush intervals may lead to latency spikes when the flush does occur as there will be a lot of data to flush.
#    3. Throughput: The flush is generally the most expensive operation, and a small flush interval may lead to exceessive seeks.
# The settings below allow one to configure the flush policy to flush data after a period of time or
# every N messages (or both). This can be done globally and overridden on a per-topic basis.

# The number of messages to accept before forcing a flush of data to disk
#log.flush.interval.messages=10000

# The maximum amount of time a message can sit in a log before we force a flush
#log.flush.interval.ms=1000

############################# Log Retention Policy #############################

# The following configurations control the disposal of log segments. The policy can
# be set to delete segments after a period of time, or after a given size has accumulated.
# A segment will be deleted whenever *either* of these criteria are met. Deletion always happens
# from the end of the log.

# The minimum age of a log file to be eligible for deletion due to age
log.retention.hours=1

# A size-based retention policy for logs. Segments are pruned from the log as long as the remaining
# segments don't drop below log.retention.bytes. Functions independently of log.retention.hours.
#log.retention.bytes=1073741824

# The maximum size of a log segment file. When this size is reached a new log segment will be created.
log.segment.bytes=1073741824

# The interval at which log segments are checked to see if they can be deleted according
# to the retention policies
log.retention.check.interval.ms=30000

############################# Zookeeper #############################

# Zookeeper connection string (see zookeeper docs for details).
# This is a comma separated host:port pairs, each corresponding to a zk
# server. e.g. "127.0.0.1:3000,127.0.0.1:3001,127.0.0.1:3002".
# You can also append an optional chroot string to the urls to specify the
# root directory for all kafka znodes.
zookeeper.connect=zkafka01vdc-int:2181,zkafka02vdc-int:2181,zkafka03vdc-int:2181

# Timeout in ms for connecting to zookeeper
zookeeper.connection.timeout.ms=6000


############################# Group Coordinator Settings #############################

# The following configuration specifies the time, in milliseconds, that the GroupCoordinator will delay the initial consumer rebalance.
# The rebalance will be further delayed by the value of group.initial.rebalance.delay.ms as new members join the group, up to a maximum of max.poll.interval.ms.
# The default value for this is 3 seconds.
# We override this to 0 here as it makes for a better out-of-the-box experience for development and testing.
# However, in production environments the default value of 3 seconds is more suitable as this will help to avoid unnecessary, and potentially expensive, rebalances during application startup.
group.initial.rebalance.delay.ms=0
mike
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F.Lazarescu
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2 Answers2

0

Remember that the retention time is not a hard upper limit but more a lower bound for your message to stay in a topic. It is important to note that messages out of an active segment will never be deleted out of a topic, even if the message exceeds the retention time. More details can be found in data still remains in kafka topic even after retention time

In Kafka you can set the retention time either by a cluster wide setting or by a topic specific setting. If you do not specify a topic specific value when creating the topic, the cluster wide setting serves as default.

In the Kafka documentation on Topic Configs it is written:

retention.ms: This configuration controls the maximum time we will retain a log before we will discard old log segments to free up space if we are using the "delete" retention policy. This represents an SLA on how soon consumers must read their data. If set to -1, no time limit is applied.

Type:                       long
Default:                    604800000
Valid Values:               [-1,...]
Server Default Property:    log.retention.ms
Importance:                 medium

It you do not set this, the log.retention.ms (or log.retention.hours) will be used.

mike
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  • Thank you for the answer. But how it's possible the retention that I just wrote? Having that value in properties file of 1 hour and no overwrite retention on the topic? From your answer I can't figure out. In the property file I don't have retention.ms – F.Lazarescu Jul 27 '20 at 11:56
  • How do you know then that the retention times are exactly 1 week and 1 day? – mike Jul 27 '20 at 12:15
  • At the client side, I'm changing the cliend-id and group-id in order to drag all the files again, from the begining. I did this on different days and it's the same. For one I see last 7 days and for one around 1 day (I say around, because it seems that it see files only from the morning) – F.Lazarescu Jul 27 '20 at 12:16
  • In that case, I guess we are talking here about the cleanup policy and active/inactive segments in your topic. – mike Jul 27 '20 at 12:18
  • As a suggestion, try to rephrase the part in your question "have retention 1 day and digital-lengid 1 week?" to reflect your observations. As you explained here in the comments it does not seems to be a hard setting but rather an assumption based on your observation. Both answers given so far made the assumption that it is a given fact that the retention times are 1 day and 1 week. – mike Jul 27 '20 at 12:26
  • Yes, you are right, thank you. I edited the question and also added the full server.properties file – F.Lazarescu Jul 27 '20 at 12:30
0

You can run the following commands in order to set per-topic retention configuration:

bin/kafka-configs.sh \
    --zookeeper 192.168.163.71:2181 \
    --alter \
    --entity-type topics \
    --entity-name digital-onboarding \
    --add-config retention.hours=24

and

bin/kafka-configs.sh \
    --zookeeper 192.168.163.71:2181 \
    --alter \
    --entity-type topics \
    --entity-name digital-lengid  \
    --add-config retention.hours=168

Once changed, you can verify that the configuration is effective by describing the topic:

bin/kafka-topics.sh \
    --zookeeper 192.168.163.71:2181 
    --describe \
    --topic digital-onboarding

The new retention policy should be listed under Configs:

Giorgos Myrianthous
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  • Hi. Thank you! I don't want to change the retention time. I need to understand why is 1 day on a topic and 7 day on another topic. Please read again my question. – F.Lazarescu Jul 27 '20 at 11:57