SET with expiry (EX, PX) in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a key with a 10-second expiry using the EX option.

Redis

SET mykey myvalue [1] 10

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

ANX

BEX

CPX

DXX

Attempts:

3 left

💡 Hint

Common Mistakes

Using PX instead of EX for seconds expiry.

Omitting the expiry option entirely.

The EX option sets the expiry time in seconds. Here, 10 means the key expires after 10 seconds.

2fill in blank

medium

Complete the code to set a key with a 5000-millisecond expiry using the PX option.

Redis

SET session_token abc123 [1] 5000

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

APX

BNX

CEX

DKEEPTTL

Attempts:

3 left

💡 Hint

Common Mistakes

Using EX instead of PX for millisecond expiry.

Forgetting to specify expiry option.

The PX option sets the expiry time in milliseconds. 5000 means the key expires after 5 seconds.

3fill in blank

hard

Fix the error in the command to set a key with a 20-second expiry using the correct expiry option.

Redis

SET user_id 42 [1] 20

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

APX

BXX

CEX

DNX

Attempts:

3 left

💡 Hint

Common Mistakes

Using PX instead of EX for seconds expiry.

Using NX or XX which control key existence, not expiry.

The EX option is correct for setting expiry in seconds. PX would interpret 20 as milliseconds, which is too short.

4fill in blank

hard

Fill both blanks to set a key with a 3000-millisecond expiry and only if the key does not exist.

Redis

SET cache_key data [1] 3000 [2]

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

APX

BEX

CNX

DXX

Attempts:

3 left

💡 Hint

Common Mistakes

Using EX instead of PX for milliseconds.

Using XX instead of NX for key existence condition.

PX sets expiry in milliseconds. NX ensures the key is set only if it does not exist.

5fill in blank

hard

Fill all three blanks to set a key with a 15-second expiry, only if the key exists, and keep the existing TTL if no expiry is given.

Redis

SET config_value 100 [1] 15 [2] [3]

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

AEX

BPX

CXX

DKEEPTTL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NX instead of XX for key existence condition.

Using PX instead of EX for seconds expiry.

Omitting KEEPTTL when wanting to keep TTL.

EX sets expiry in seconds. XX means set only if key exists. KEEPTTL keeps the existing TTL if no new expiry is specified.

Practice

1. What does the EX option do when used with the Redis SET command?

easy

A. Sets the key to expire after a specified number of seconds

B. Sets the key to expire after a specified number of milliseconds

C. Sets the key without any expiration

D. Deletes the key immediately after setting it

Solution

1. Step 1: Understand the EX option in Redis SET

   The EX option sets the expiration time in seconds for the key.

2. Step 2: Compare EX with other expiry options

   PX sets expiry in milliseconds, so EX is specifically for seconds.

3. Final Answer:

   Sets the key to expire after a specified number of seconds -> Option A

4. Quick Check:

   EX = seconds expiry [OK]

Hint: EX means seconds expiry, PX means milliseconds expiry [OK]

Common Mistakes:

• Confusing EX with PX and thinking EX is milliseconds
• Assuming EX sets no expiry
• Thinking EX deletes the key immediately

2. Which of the following is the correct syntax to set a key session with value abc123 that expires in 10 seconds using Redis?

easy

A. SET session abc123 EXPIRE 10

B. SET session EX 10 abc123

C. SET session abc123 PX 10

D. SET session abc123 EX 10

Solution

1. Step 1: Recall Redis SET command syntax with expiry

   The correct syntax is: SET key value EX seconds.

2. Step 2: Check each option for correct order and keyword

   SET session abc123 EX 10 matches the correct order and uses EX for seconds expiry.

3. Final Answer:

   SET session abc123 EX 10 -> Option D

4. Quick Check:

   SET key value EX seconds = correct syntax [OK]

Hint: Remember: SET key value EX seconds [OK]

Common Mistakes:

• Placing EX before the value
• Using PX instead of EX for seconds
• Using EXPIRE keyword inside SET command

3. What will be the output of the following Redis commands executed in order?

SET temp 100 PX 5000
TTL temp

medium

A. An integer close to 5

B. 5

C. 0

D. -1

Solution

1. Step 1: Understand PX expiry in SET command

   PX 5000 sets the key to expire in 5000 milliseconds (5 seconds).

2. Step 2: Interpret TTL command output

   TTL returns time to live in seconds. Since expiry was set in milliseconds, TTL rounds to nearest second.

3. Step 3: Predict TTL value

   TTL will return an integer close to 5 seconds, depending on execution time.

4. Final Answer:

   An integer close to 5 -> Option A

5. Quick Check:

   PX 5000 ms = ~5 seconds TTL [OK]

Hint: TTL returns seconds even if PX used for expiry [OK]

Common Mistakes:

• Expecting TTL to return milliseconds
• Thinking TTL returns 0 immediately
• Assuming TTL returns -1 for keys with expiry

4. Identify the error in this Redis command:

SET user123 "John" EXPIRE 20

medium

A. Value should not be in quotes

B. EXPIRE is not valid inside SET command

C. Missing quotes around key

D. EXPIRE should be PX for milliseconds

Solution

1. Step 1: Check Redis SET command syntax

   SET command uses EX or PX for expiry, not EXPIRE keyword.

2. Step 2: Identify misuse of EXPIRE keyword

   EXPIRE is a separate command, not an option inside SET.

3. Final Answer:

   EXPIRE is not valid inside SET command -> Option B

4. Quick Check:

   Use EX or PX inside SET, not EXPIRE [OK]

Hint: Use EX or PX with SET, EXPIRE is separate command [OK]

Common Mistakes:

• Using EXPIRE inside SET command
• Confusing EXPIRE command with expiry option
• Misplacing quotes around key or value

5. You want to store a temporary API token in Redis that expires exactly after 1500 milliseconds. Which command correctly sets the key api_token with value xyz789 and the required expiry?

hard

A. SET api_token xyz789 EX 1.5

B. SET api_token xyz789 EX 1500

C. SET api_token xyz789 PX 1500

D. SET api_token xyz789 PX 1.5

Solution

1. Step 1: Determine correct expiry option for milliseconds

   PX sets expiry in milliseconds, EX uses seconds only.

2. Step 2: Check value format for PX

   PX requires integer milliseconds, so 1500 is valid, decimals like 1.5 are invalid.

3. Step 3: Validate each option

   SET api_token xyz789 PX 1500 uses PX 1500 correctly; others use wrong units or decimals.

4. Final Answer:

   SET api_token xyz789 PX 1500 -> Option C

5. Quick Check:

   Milliseconds expiry = PX integer value [OK]

Hint: Use PX with integer milliseconds for precise expiry [OK]

Common Mistakes:

• Using EX with decimal seconds
• Using PX with decimal instead of integer
• Confusing EX and PX units