Why patterns guide Redis usage - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a key-value pair in Redis.

Redis

SET [1] "Hello"

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

ADEL

BGET

Cgreeting

DEXPIRE

Attempts:

3 left

💡 Hint

Common Mistakes

Using a command like GET instead of a key name.

Leaving the key blank.

The SET command stores a value under a key. Here, the key should be a name like greeting.

2fill in blank

medium

Complete the code to retrieve the value of a key in Redis.

Redis

GET [1]

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

Agreeting

BDEL

Cvalue

DSET

Attempts:

3 left

💡 Hint

Common Mistakes

Using a command name instead of a key.

Using a different key name than the one stored.

The GET command retrieves the value stored under the given key. Here, the key is greeting.

3fill in blank

hard

Fix the error in the code to delete a key in Redis.

Redis

DEL [1]

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

AGET

BEXPIRE

CSET

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Using a command name instead of a key.

Trying to delete a key that does not exist.

The DEL command deletes the key and its value. You must specify the key name, here greeting.

4fill in blank

hard

Fill both blanks to set a key with an expiration time in seconds.

Redis

SET [1] "SessionData" [2] 300

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

Asession_key

BEX

CPX

DDEL

Attempts:

3 left

💡 Hint

Common Mistakes

Using PX instead of EX for seconds.

Using a command name instead of a key.

The SET command can take EX to set expiration time in seconds. The key name here is session_key.

5fill in blank

hard

Fill all three blanks to add a member with a score to a sorted set in Redis.

Redis

ZADD [1] [2] [3]

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

Aleaderboard

B1500

Cplayer1

Dsession

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of score and member.

Using a wrong key name or command instead of the set name.

The ZADD command adds a member with a score to a sorted set. Here, leaderboard is the set name, 1500 is the score, and player1 is the member.

Practice

1. Why is it important to follow usage patterns when working with Redis?

easy

A. Because patterns help solve common problems efficiently

B. Because Redis only supports one command

C. Because patterns make Redis slower

D. Because patterns limit Redis features

Solution

1. Step 1: Understand Redis usage patterns

   Patterns are proven ways to use Redis commands together to solve common problems like caching and queues.

2. Step 2: Recognize the benefit of patterns

   Using patterns makes your app faster and simpler by avoiding reinventing solutions.

3. Final Answer:

   Because patterns help solve common problems efficiently -> Option A

4. Quick Check:

   Patterns guide Redis usage = Efficient problem solving [OK]

Hint: Patterns solve common Redis problems efficiently [OK]

Common Mistakes:

• Thinking Redis supports only one command
• Believing patterns slow down Redis
• Assuming patterns limit Redis features

2. Which of the following is the correct Redis command syntax to add a member to a set?

easy

A. ADDSET myset member1

B. ADD myset member1

C. SETADD myset member1

D. SADD myset member1

Solution

1. Step 1: Recall Redis set command syntax

   The correct command to add a member to a set is SADD key member.

2. Step 2: Match the options

   Only SADD myset member1 uses SADD correctly with key and member.

3. Final Answer:

   SADD myset member1 -> Option D

4. Quick Check:

   SADD adds member to set [OK]

Hint: Remember Redis set add command is SADD [OK]

Common Mistakes:

• Using ADDSET or SETADD which are invalid commands
• Using ADD which is not a Redis command

3. Given the following Redis commands executed in order:

INCR page_views
INCR page_views
GET page_views

What will be the output of the GET page_views command?

medium

A. 0

B. 1

C. 2

D. Error

Solution

1. Step 1: Understand INCR command effect

   Each INCR command increases the integer value stored at the key by 1, starting from 0 if key does not exist.

2. Step 2: Calculate the value after two INCR commands

   After two INCR commands, the value is 2.

3. Step 3: GET command returns the current value

   GET page_views returns the string "2" representing the number.

4. Final Answer:

   2 -> Option C

5. Quick Check:

   Two INCRs then GET = 2 [OK]

Hint: INCR twice then GET returns 2 [OK]

Common Mistakes:

• Assuming INCR starts from 1 instead of 0
• Expecting GET to return integer type instead of string
• Thinking GET returns error if key was not set before

4. You wrote this Redis command to add a member to a sorted set:

ZADD myzset member1 10

But it returns an error. What is the mistake?

medium

A. The command should be 'ZADD myzset member1' without score

B. The score and member order is reversed; it should be 'ZADD myzset 10 member1'

C. Sorted sets do not support ZADD command

D. The key name 'myzset' is invalid

Solution

1. Step 1: Recall ZADD syntax

   ZADD command syntax is: ZADD key score member [score member ...]. The score must come before the member.

2. Step 2: Identify the error in command

   The command uses 'member1 10' which reverses the order; it should be '10 member1'.

3. Final Answer:

   The score and member order is reversed; it should be 'ZADD myzset 10 member1' -> Option B

4. Quick Check:

   ZADD syntax = ZADD key score member [OK]

Hint: ZADD needs score before member [OK]

Common Mistakes:

• Swapping score and member order
• Omitting score for sorted set member
• Thinking ZADD is unsupported for sorted sets

5. You want to implement a simple queue using Redis commands. Which pattern correctly uses Redis to enqueue and dequeue items?

hard

A. Use LPUSH to add items and RPOP to remove items (FIFO queue)

B. Use SADD to add items and SPOP to remove items (FIFO queue)

C. Use SET to add items and GET to remove items (FIFO queue)

D. Use ZADD to add items and ZREM to remove items (FIFO queue)

Solution

1. Step 1: Identify Redis commands for queue pattern

   Redis lists support LPUSH (add to left) and RPOP (remove from right) to implement FIFO queues.

2. Step 2: Evaluate other options

   SADD and SPOP work on sets (unordered), SET/GET are key-value, ZADD/ZREM are for sorted sets (not FIFO).

3. Final Answer:

   Use LPUSH to add items and RPOP to remove items (FIFO queue) -> Option A

4. Quick Check:

   LPUSH + RPOP = FIFO queue [OK]

Hint: Use LPUSH and RPOP for FIFO queue in Redis [OK]

Common Mistakes:

• Using sets which are unordered for queues
• Using SET/GET which overwrite keys
• Using sorted sets which are not FIFO by default