Why consumers process messages in Kafka - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to consume messages from a Kafka topic.

Kafka

from kafka import KafkaConsumer

consumer = KafkaConsumer('[1]', bootstrap_servers=['localhost:9092'])
for message in consumer:
    print(message.value)

Drag options to blanks, or click blank then click option'

Amy_topic

Bproducer

Cbroker

Dpartition

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'producer' or 'broker' instead of the topic name.

Leaving the topic name blank.

The consumer must subscribe to the correct topic name to receive messages. Here, 'my_topic' is the topic name.

2fill in blank

medium

Complete the code to decode the message value as UTF-8 string.

Kafka

for message in consumer:
    text = message.value.[1]('utf-8')
    print(text)

Drag options to blanks, or click blank then click option'

Asplit

Bstrip

Cdecode

Dencode

Attempts:

3 left

💡 Hint

Common Mistakes

Using encode instead of decode.

Trying to print bytes directly without decoding.

Message values are bytes and need to be decoded to strings using decode('utf-8').

3fill in blank

hard

Fix the error in the code to commit the message offset manually.

Kafka

for message in consumer:
    print(message.value.decode('utf-8'))
    consumer.[1]()

Drag options to blanks, or click blank then click option'

Acommit

Bcommit_async

Ccommit_offsets

Dcommit_sync

Attempts:

3 left

💡 Hint

Common Mistakes

Using the synchronous 'commit()' method.

Using 'commit_sync' which is not a valid method.

To commit offsets manually in KafkaConsumer, use commit_async() for asynchronous commits.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each word to its length only if the length is greater than 3.

Kafka

words = ['apple', 'bat', 'car', 'door']
lengths = {word: [1] for word in words if len(word) [2] 3}

Drag options to blanks, or click blank then click option'

Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Mapping word to word instead of its length.

The dictionary comprehension maps each word to its length using len(word) and filters words with length greater than 3 using >.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase words to their values only if the value is greater than 0.

Kafka

data = {'apple': 5, 'bat': 0, 'car': 3}
result = { [1]: [2] for k, v in data.items() if v [3] 0 }

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

C>

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'k' instead of 'k.upper()' for keys.

Using '<' instead of '>' in the condition.

The comprehension maps uppercase keys k.upper() to their values v only if v > 0.

Practice

1. Why do Kafka consumers process messages from topics?

easy

A. To create new topics automatically

B. To read and use data sent by producers

C. To delete messages from the topic

D. To send messages to other consumers

Solution

1. Step 1: Understand the role of consumers in Kafka

   Consumers read messages produced by producers to get data for processing.

2. Step 2: Identify the purpose of processing messages

   Processing messages allows applications to react to new information sent by producers.

3. Final Answer:

   To read and use data sent by producers -> Option B

4. Quick Check:

   Consumers read messages = To use data [OK]

Hint: Consumers read messages to get data from producers [OK]

Common Mistakes:

• Thinking consumers send messages
• Confusing consumers with producers
• Believing consumers delete messages

2. Which of the following is the correct way for a Kafka consumer to subscribe to a topic named orders in Java?

easy

A. consumer.listen("orders");

B. consumer.subscribe("orders");

C. consumer.connect("orders");

D. consumer.subscribe(Collections.singletonList("orders"));

Solution

1. Step 1: Recall Kafka consumer subscription syntax in Java

   The consumer.subscribe method expects a collection of topic names, usually a list.

2. Step 2: Check each option's syntax

   consumer.subscribe(Collections.singletonList("orders")); uses Collections.singletonList("orders"), which is correct. Options A, B, and D use incorrect methods or argument types.

3. Final Answer:

   consumer.subscribe(Collections.singletonList("orders")); -> Option D

4. Quick Check:

   subscribe needs a list of topics [OK]

Hint: Use subscribe with a list of topics in Java [OK]

Common Mistakes:

• Passing a string instead of a list
• Using non-existent methods like listen or connect
• Forgetting to import Collections

3. Given the following Kafka consumer code snippet in Python, what will be printed?

from kafka import KafkaConsumer

consumer = KafkaConsumer('test-topic', bootstrap_servers=['localhost:9092'])
for message in consumer:
    print(message.value.decode('utf-8'))
    break

medium

A. The first message's value from 'test-topic' decoded as UTF-8

B. All messages from 'test-topic' printed continuously

C. An error because decode is not a method

D. No output because the loop breaks immediately

Solution

1. Step 1: Understand the consumer loop behavior

   The for loop reads messages from 'test-topic' one by one.

2. Step 2: Analyze the print and break statements

   The first message's value is decoded from bytes to string and printed, then the loop breaks immediately.

3. Final Answer:

   The first message's value from 'test-topic' decoded as UTF-8 -> Option A

4. Quick Check:

   Print first message then break = first message only [OK]

Hint: Loop breaks after first message, so only one prints [OK]

Common Mistakes:

• Thinking all messages print
• Confusing decode method usage
• Assuming no output due to break

4. What is wrong with this Kafka consumer code snippet in Java?

KafkaConsumer consumer = new KafkaConsumer<>(props);
consumer.subscribe("my-topic");
while(true) {
    ConsumerRecords records = consumer.poll(Duration.ofMillis(100));
    for (ConsumerRecord record : records) {
        System.out.println(record.value());
    }
}

medium

A. poll method should not have a timeout argument

B. ConsumerRecord does not have a value() method

C. subscribe method requires a collection, not a single string

D. The while loop should be replaced with a for loop

Solution

1. Step 1: Check the subscribe method usage

   In Kafka Java client, subscribe expects a collection of topic names, not a single string.

2. Step 2: Verify other code parts

   poll with Duration is correct, ConsumerRecord has value(), and while(true) is valid for continuous consumption.

3. Final Answer:

   subscribe method requires a collection, not a single string -> Option C

4. Quick Check:

   subscribe needs list of topics [OK]

Hint: subscribe needs a list, not a single string [OK]

Common Mistakes:

• Passing a string directly to subscribe
• Misunderstanding poll method arguments
• Thinking ConsumerRecord lacks value()

5. You want your Kafka consumer to process messages only from the latest offset to react quickly to new data. Which consumer configuration should you set before subscribing?

hard

A. "auto.offset.reset" to "latest"

B. "enable.auto.commit" to false

C. "group.id" to a unique value each time

D. "max.poll.records" to 1

Solution

1. Step 1: Understand offset reset behavior

   Setting "auto.offset.reset" to "latest" makes the consumer start reading from the newest messages if no committed offset exists.

2. Step 2: Evaluate other options

   "enable.auto.commit" controls offset commits, "group.id" identifies consumer groups, and "max.poll.records" limits batch size but doesn't affect starting offset.

3. Final Answer:

   "auto.offset.reset" to "latest" -> Option A

4. Quick Check:

   Start from latest messages = auto.offset.reset=latest [OK]

Hint: Set auto.offset.reset to latest to read newest messages [OK]

Common Mistakes:

• Confusing offset reset with auto commit
• Changing group.id to control offset start
• Using max.poll.records to control offset