Message queue concept in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a message queue that stores messages in a FIFO order.

HLD

message_queue = [1]()

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

AStack

BQueue

CList

DSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using a Stack instead of a Queue causes last-in-first-out behavior.

Using a Set loses message order.

The message queue should use a FIFO structure, which is provided by a Queue.

2fill in blank

medium

Complete the code to add a message to the queue.

HLD

message_queue.[1](message)

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

Aenqueue

Bpop

Cput

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop removes messages instead of adding.

Using enqueue is not a standard method name in Python's queue.

In many queue implementations, the method to add an item is called put.

3fill in blank

hard

Fix the error in the code to retrieve a message from the queue without removing it.

HLD

next_message = message_queue.[1]()

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

Apeek

Bget

Cpop

Dfront

Attempts:

3 left

💡 Hint

Common Mistakes

Using get removes the message from the queue.

Using pop removes the message and is not a standard queue method.

The peek method allows viewing the next message without removing it, which is needed here.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps message IDs to their content for messages longer than 5 characters.

HLD

{msg.id: msg.[1] for msg in messages if len(msg.[2]) > 5}

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

Acontent

Bid

Ctext

Dbody

Attempts:

3 left

💡 Hint

Common Mistakes

Using the message ID as the value instead of the content.

Checking length on the ID instead of the message text.

The dictionary maps message IDs to their content. The content is accessed by content and the length check uses body.

5fill in blank

hard

Fill all three blanks to create a filtered dictionary of messages where the content length is greater than 10 and keys are uppercase IDs.

HLD

{msg.[1].upper(): msg.[2] for msg in messages if len(msg.[3]) > 10}

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

Aid

Bcontent

Cbody

Dupper

Attempts:

3 left

💡 Hint

Common Mistakes

Using content as the key instead of the value.

Checking length on the content instead of the body.

The keys are uppercase message IDs, so id with upper() is used. The values are the content, and the length check is on the body.

Practice

1. What is the primary purpose of a message queue in system design?

easy

A. To speed up the CPU processing directly

B. To permanently save all data for backup

C. To replace the database in storing user information

D. To store messages temporarily until the receiver is ready to process them

Solution

1. Step 1: Understand message queue role

   A message queue acts as a temporary storage for messages between systems or components.

2. Step 2: Identify correct purpose

   It holds messages safely until the receiver can process them, helping with speed differences and reliability.

3. Final Answer:

   To store messages temporarily until the receiver is ready to process them -> Option D

4. Quick Check:

   Message queue = Temporary message storage [OK]

Hint: Message queues hold messages until processing [OK]

Common Mistakes:

• Thinking message queues permanently store data
• Confusing message queues with databases
• Assuming message queues speed up CPU directly

2. Which of the following is the correct way to describe a FIFO queue behavior in a message queue?

easy

A. Messages are processed in random order

B. Messages are processed in the order they arrive

C. Messages are processed starting from the largest size

D. Messages are processed only when the queue is full

Solution

1. Step 1: Define FIFO in message queues

   FIFO means First In, First Out, so messages are handled in the order they arrive.

2. Step 2: Match FIFO behavior to options

   Only Messages are processed in the order they arrive describes processing messages in arrival order, matching FIFO.

3. Final Answer:

   Messages are processed in the order they arrive -> Option B

4. Quick Check:

   FIFO = Process in arrival order [OK]

Hint: FIFO means first message goes out first [OK]

Common Mistakes:

• Confusing FIFO with random or size-based order
• Thinking queue processes only when full
• Mixing FIFO with LIFO (Last In First Out)

3. Consider a message queue system where messages arrive at 10 per second and are processed at 8 per second. What will happen over time?

medium

A. The queue will shrink because processing rate is faster

B. The queue will stay stable because arrival and processing rates are equal

C. The queue will grow indefinitely because arrival rate > processing rate

D. The queue will empty immediately after first message

Solution

1. Step 1: Compare arrival and processing rates

   Messages arrive at 10 per second but only 8 are processed per second.

2. Step 2: Analyze queue growth

   Since arrival rate is higher, messages accumulate, making the queue grow over time.

3. Final Answer:

   The queue will grow indefinitely because arrival rate > processing rate -> Option C

4. Quick Check:

   Arrival > Processing = Queue grows [OK]

Hint: If arrival > processing, queue grows [OK]

Common Mistakes:

• Assuming queue stays stable despite higher arrival rate
• Thinking processing rate is faster than arrival
• Ignoring queue growth over time

4. A message queue system is dropping messages unexpectedly. Which of the following is the most likely cause?

medium

A. The queue size limit is too small and messages are discarded when full

B. The messages are processed faster than they arrive

C. The queue uses FIFO order correctly

D. The system has infinite storage capacity

Solution

1. Step 1: Identify reason for message drops

   Messages drop usually when the queue is full and cannot accept new messages.

2. Step 2: Match cause to options

   The queue size limit is too small and messages are discarded when full states the queue size is too small causing discards, which explains drops.

3. Final Answer:

   The queue size limit is too small and messages are discarded when full -> Option A

4. Quick Check:

   Small queue size = message drops [OK]

Hint: Full queue causes message drops [OK]

Common Mistakes:

• Assuming faster processing causes drops
• Ignoring queue size limits
• Thinking infinite storage exists

5. You need to design a message queue system for a high-traffic online store where orders must be processed reliably and in order. Which design choice best supports this requirement?

hard

A. Use a distributed FIFO queue with message persistence and retry mechanisms

B. Use an in-memory queue without persistence for faster speed

C. Use a random order queue to balance load evenly

D. Use a queue that drops messages when overloaded to avoid delays

Solution

1. Step 1: Understand requirements for reliability and order

   The system must process orders reliably and maintain the order of messages.

2. Step 2: Evaluate design options

   A distributed FIFO queue ensures order, persistence prevents data loss, and retries handle failures.

3. Step 3: Eliminate unsuitable options

   In-memory queues risk data loss, random order breaks order, and dropping messages harms reliability.

4. Final Answer:

   Use a distributed FIFO queue with message persistence and retry mechanisms -> Option A

5. Quick Check:

   Reliable ordered processing = distributed FIFO + persistence [OK]

Hint: Reliable order needs FIFO + persistence + retries [OK]

Common Mistakes:

• Choosing in-memory queues risking data loss
• Ignoring message order importance
• Allowing message drops under load