kafka [My wiki]

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=====Overview=====
Apache Kafka is an open-source stream-processing software platform developed by the Apache Software Foundation, written in Scala and Java. The project aims to provide a unified, high-throughput, low-latency platform for handling real-time data feeds.

In a nutshell, you say data to it and you can do something with that data. Here we will process data from Oracle through Kafka to big data.

So for example, you can have: Oracle -> Kafka -> Hadoop/Hbase

For that, Kafka has two sets of clients:

  * Producers - Clients who procedure / import data into Kafka
  * Consumers - Clients who consume / read the data from Kafka


{{ :kafkaarch.png?400 |}}

=====Management=====
To start Kafka, we can use the following script:

<Code:bash|Start Kafka>
[oracle@edvmr1p0 ~]$ kafka-server-start.sh
USAGE: /opt/kafka/bin/kafka-server-start.sh [-daemon] server.properties [--override property=value]*
[oracle@edvmr1p0 ~]$ kafka-server-start.sh $KAFKA_HOME/config/server.properties
[2020-11-11 09:33:54,319] INFO KafkaConfig values: 
	advertised.host.name = null
	metric.reporters = []
	quota.producer.default = 9223372036854775807
	offsets.topic.num.partitions = 50
	log.flush.interval.messages = 9223372036854775807
	auto.create.topics.enable = true
	controller.socket.timeout.ms = 30000
	log.flush.interval.ms = null
	principal.builder.class = class org.apache.kafka.common.security.auth.DefaultPrincipalBuilder
	replica.socket.receive.buffer.bytes = 65536
	min.insync.replicas = 1
.........
</Code>

====Create a topic====
To create a topic we can use teh following command, knowing the zookeeper port and the name of the topic of course:

<Code:bash|Create Topic>
[oracle@edvmr1p0 config]$ kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 -topic ogg12cBigData
Created topic "ogg12cBigData".
</Code>


====Send message to Kafka====
Sending messages to Kafka is easy once you know the broker list and the topic to which you want them sent:


<Code:bash|Send message to Kafka>
[oracle@edvmr1p0 config]$ kafka-console-producer.sh --broker-list localhost:9092 --topic ogg12cBigData
Testing Kafka in the context of OGG 12c for Big Data                  <- First Message

Second message sent to the Kafka cluster                              <- Second Message
</Code>


====Consume message====
To consume / read a message from Kafka, we can use the following command:


<Code:bash|Consume/Read Message>
[oracle@edvmr1p0 config]$ kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic ogg12cBigData --from-beginning --zookeeper localhost:2181
Testing Kafka in the context of OGG 12c for Big Data
Second message sent to the Kafka cluster

Second message sent to the Kafka cluster
</Code>

=====Appendix=====
<Code:bash|Kafka server.properties>
# 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=0
port=9092
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 = security_protocol://host_name:port
#   EXAMPLE:
#     listeners = PLAINTEXT://your.host.name:9092
#listeners=PLAINTEXT://:9092

# 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://your.host.name:9092

# The number of threads handling network requests
num.network.threads=3

# The number of threads doing 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=/tmp/kafka-logs

# 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

############################# 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
log.retention.hours=168

# 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.
#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=300000

############################# 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=localhost:2181

# Timeout in ms for connecting to zookeeper
zookeeper.connection.timeout.ms=6000
</Code>