Join operations (KStream-KStream, KStream-KTable) in Kafka - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to join two KStreams by key using an inner join.

Kafka

KStream<String, String> joinedStream = stream1.[1](stream2, (value1, value2) -> value1 + value2, JoinWindows.of(Duration.ofMinutes(5)), Joined.with(Serdes.String(), Serdes.String(), Serdes.String()));

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

Afilter

BleftJoin

Cjoin

DouterJoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using leftJoin instead of join causes a different join behavior.

Using filter does not perform a join.

The join method performs an inner join between two KStreams based on their keys.

2fill in blank

medium

Complete the code to join a KStream with a KTable using a left join.

Kafka

KStream<String, String> joinedStream = stream.[1](table, (streamValue, tableValue) -> streamValue + (tableValue == null ? "" : tableValue));

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

Ajoin

Bfilter

CouterJoin

DleftJoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using join instead of leftJoin excludes stream records without matching table keys.

Using outerJoin is not supported between KStream and KTable.

The leftJoin method joins a KStream with a KTable, including all records from the stream even if the table has no matching key.

3fill in blank

hard

Fix the error in the join window definition for a KStream-KStream join.

Kafka

KStream<String, String> joinedStream = stream1.join(stream2, (v1, v2) -> v1 + v2, JoinWindows.[1](Duration.ofMinutes(10)), Joined.with(Serdes.String(), Serdes.String(), Serdes.String()));

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Aof

BofTimeDifferenceWithNoGrace

CwithTimeDifferenceAndGrace

DofMillis

Attempts:

3 left

💡 Hint

Common Mistakes

Using deprecated or incorrect window methods causes runtime errors.

Using ofMillis expects a long, not a Duration.

The JoinWindows.of(Duration) method defines the join window duration correctly for KStream-KStream joins.

4fill in blank

hard

Fill both blanks to create a KStream-KTable join with correct Serdes and join type.

Kafka

KStream<String, String> result = stream.[1](table, (sValue, tValue) -> sValue + tValue, Joined.with(Serdes.[2], Serdes.String(), Serdes.String()));

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

AleftJoin

Bjoin

CString

DInteger

Attempts:

3 left

💡 Hint

Common Mistakes

Using join instead of leftJoin excludes stream records without matching keys.

Using Integer serde for string keys causes serialization errors.

The leftJoin method is used for KStream-KTable joins including all stream records. The key serde is Serdes.String() for string keys.

5fill in blank

hard

Fill all three blanks to create a KStream-KStream join with a 5-minute window and correct join type and serde.

Kafka

KStream<String, String> joined = stream1.[1](stream2, (v1, v2) -> v1 + v2, JoinWindows.[2](Duration.ofMinutes(5)), Joined.with(Serdes.[3], Serdes.String(), Serdes.String()));

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

Ajoin

BleftJoin

Cof

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using leftJoin instead of join changes join semantics.

Using incorrect window method causes errors.

Using wrong serde causes serialization issues.

Use join for KStream-KStream inner join, JoinWindows.of(Duration) to set the window, and Serdes.String() for string keys.

Practice

1. What is the main difference between a KStream-KStream join and a KStream-KTable join in Kafka Streams?

easy

A. KStream-KStream joins require a time window; KStream-KTable joins do not.

B. KStream-KTable joins require a time window; KStream-KStream joins do not.

C. Both joins require a time window to match records.

D. Neither join requires a time window.

Solution

1. Step 1: Understand KStream-KStream join behavior

   KStream-KStream joins combine records from two streams that occur within a specified time window.

2. Step 2: Understand KStream-KTable join behavior

   KStream-KTable joins enrich stream records with the latest matching table record without needing a time window.

3. Final Answer:

   KStream-KStream joins require a time window; KStream-KTable joins do not. -> Option A

4. Quick Check:

   Time window needed only for KStream-KStream joins [OK]

Hint: Remember: only KStream-KStream joins need time windows [OK]

Common Mistakes:

• Confusing which join requires a time window
• Thinking both joins behave the same
• Assuming KStream-KTable join needs time window

2. Which of the following is the correct syntax to perform a KStream-KTable join in Kafka Streams?

easy

A. ktable.join(kstream, (tableValue, streamValue) -> tableValue + streamValue);

B. kstream.join(ktable, JoinWindows.of(Duration.ofMinutes(5)), (v1, v2) -> v1 + v2);

C. kstream.join(ktable, (streamValue, tableValue) -> streamValue + tableValue);

D. kstream.join(ktable, (v1, v2) -> v1 + v2, JoinWindows.of(Duration.ofMinutes(5)));

Solution

1. Step 1: Identify KStream-KTable join syntax

   KStream-KTable join uses kstream.join(ktable, ValueJoiner) without a time window.

2. Step 2: Check options for correct method signature

   kstream.join(ktable, (streamValue, tableValue) -> streamValue + tableValue); matches the correct syntax: join without window and with a ValueJoiner lambda.

3. Final Answer:

   kstream.join(ktable, (streamValue, tableValue) -> streamValue + tableValue); -> Option C

4. Quick Check:

   KStream-KTable join syntax = kstream.join(ktable, (streamValue, tableValue) -> streamValue + tableValue); [OK]

Hint: KStream-KTable join has no time window parameter [OK]

Common Mistakes:

• Adding JoinWindows to KStream-KTable join
• Reversing stream and table parameters
• Using KTable join method on KStream

3. Given the following Kafka Streams code snippet, what will be the output if the input streams have matching keys within the 5-minute window?

var joinedStream = stream1.join(stream2, (v1, v2) -> v1 + v2, JoinWindows.of(Duration.ofMinutes(5)));
joinedStream.foreach((key, value) -> System.out.println(key + ":" + value));

medium

A. Prints combined values for keys appearing in both streams within 5 minutes

B. Prints combined values for all keys in stream1 regardless of stream2

C. Prints only keys from stream2 with no combination

D. Throws a runtime exception due to missing KTable

Solution

1. Step 1: Understand KStream-KStream join with window

   The join combines records from both streams with matching keys occurring within the 5-minute window.

2. Step 2: Analyze output behavior

   For matching keys within the window, the values are combined using the lambda (v1 + v2) and printed.

3. Final Answer:

   Prints combined values for keys appearing in both streams within 5 minutes -> Option A

4. Quick Check:

   KStream-KStream join outputs combined matching keys [OK]

Hint: KStream-KStream join outputs combined values within window [OK]

Common Mistakes:

• Assuming all keys from stream1 print regardless of stream2
• Confusing KStream-KTable join behavior
• Expecting runtime error without KTable

4. Identify the error in the following Kafka Streams join code:

var joined = stream1.join(stream2, (v1, v2) -> v1 + v2);
joined.print();

medium

A. Incorrect lambda syntax for join function

B. Missing JoinWindows parameter for KStream-KStream join

C. Using print() instead of foreach() causes error

D. stream2 should be a KTable, not a KStream

Solution

1. Step 1: Check join method parameters

   KStream-KStream join requires a JoinWindows parameter to specify the time window for matching events.

2. Step 2: Identify missing parameter

   The code omits the JoinWindows argument, causing a compilation error.

3. Final Answer:

   Missing JoinWindows parameter for KStream-KStream join -> Option B

4. Quick Check:

   KStream-KStream join needs JoinWindows [OK]

Hint: KStream-KStream join always needs JoinWindows [OK]

Common Mistakes:

• Forgetting JoinWindows in KStream-KStream join
• Confusing KStream-KTable join syntax
• Assuming print() is invalid method

5. You want to enrich a stream of user clicks (KStream) with the latest user profile data stored in a KTable. Which join operation should you use and why?

hard

A. Use KStream-KStream join without a window to join clicks and profiles.

B. Use KStream-KStream join with a 10-minute window to combine clicks and profiles.

C. Use KTable-KTable join because both are tables.

D. Use KStream-KTable join to enrich clicks with latest profile data without time window.

Solution

1. Step 1: Identify data types and join needs

   User clicks are a stream (KStream), and user profiles are stored as a table (KTable).

2. Step 2: Choose appropriate join type

   KStream-KTable join enriches stream data with the latest table data for matching keys without needing a time window.

3. Final Answer:

   Use KStream-KTable join to enrich clicks with latest profile data without time window. -> Option D

4. Quick Check:

   KStream-KTable join enriches stream with latest table data [OK]

Hint: Enrich stream with table data using KStream-KTable join [OK]

Common Mistakes:

• Using KStream-KStream join unnecessarily
• Adding time window to KStream-KTable join
• Confusing KTable-KTable join for stream enrichment