Temporary data with TTL in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a key with a value in Redis.

Redis

SET mykey [1]

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

A"Hello"

BEX 10

CDEL

DGET

Attempts:

3 left

💡 Hint

Common Mistakes

Using EX 10 immediately after SET without a value.

Using DEL or GET instead of a value.

The SET command requires the key and the value. Here, the value is "Hello".

2fill in blank

medium

Complete the code to set a key with a value and an expiration time of 30 seconds.

Redis

SET mykey "Hello" [1] 30

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

APX

BTTL

CEX

DPTTL

Attempts:

3 left

💡 Hint

Common Mistakes

Using PX which sets expiration in milliseconds.

Using TTL or PTTL which are commands, not options here.

The EX option sets the expiration time in seconds.

3fill in blank

hard

Fix the error in the command to set a key with expiration of 60 seconds.

Redis

SET mykey "World" [1]

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

AEXPIRE 60

BTTL 60

CPX 60000

DEX 60

Attempts:

3 left

💡 Hint

Common Mistakes

Using TTL or EXPIRE as options in SET command.

Using PX 60000 which is milliseconds, but the question expects seconds.

The correct syntax to set expiration during SET is EX 60 for 60 seconds.

4fill in blank

hard

Fill both blanks to set a key with value and expiration in milliseconds.

Redis

SET mykey [1] [2] 15000

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

A"Temporary"

BEX

CPX

D"Permanent"

Attempts:

3 left

💡 Hint

Common Mistakes

Using EX instead of PX for milliseconds.

Using "Permanent" as value when temporary data is needed.

Use PX to set expiration in milliseconds and provide the value "Temporary".

5fill in blank

hard

Fill all three blanks to set a key with value and expiration, then check its TTL.

Redis

SET [1] [2] EX 20
TTL [3]

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

Asession_token

B"abc123"

D"xyz789"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different key names in SET and TTL commands.

Not using quotes around the value string.

Set key session_token with value "abc123" and expiration 20 seconds, then check TTL of session_token.

Practice

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

easy

A. Deletes the key immediately after setting it

B. Sets a time-to-live (TTL) in seconds for the key, after which it expires

C. Sets the key to be persistent and never expire

D. Renames the key to a new name

Solution

1. Step 1: Understand the SET command with EX option

   The SET command stores a key-value pair. The EX option specifies the expiration time in seconds.

2. Step 2: Effect of EX on the key

   When EX is used, the key will automatically be deleted after the given time passes.

3. Final Answer:

   Sets a time-to-live (TTL) in seconds for the key, after which it expires -> Option B

4. Quick Check:

   EX = TTL in seconds [OK]

Hint: EX sets expiration time in seconds for keys [OK]

Common Mistakes:

• Thinking EX makes the key permanent
• Confusing EX with immediate deletion
• Assuming EX renames the key

2. Which of the following is the correct syntax to set a key session with value abc123 that expires in 120 seconds in Redis?

easy

A. SET session abc123 PX 120

B. SET session EX 120 abc123

C. SET EX 120 session abc123

D. SET session abc123 EX 120

Solution

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

   The correct syntax is SET key value EX seconds.

2. Step 2: Match the syntax with options

   SET session abc123 EX 120 matches the correct order: key, value, EX, seconds.

3. Final Answer:

   SET session abc123 EX 120 -> Option D

4. Quick Check:

   SET key value EX seconds [OK]

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

Common Mistakes:

• Placing EX before the key or value
• Using PX instead of EX for seconds
• Mixing order of arguments

3. Given the commands below, what will be the output of TTL user:123 immediately after execution?

SET user:123 "John" EX 60
TTL user:123

medium

A. 60

B. -1

C. -2

D. 0

Solution

1. Step 1: Understand the SET with EX 60

   The key user:123 is set with a TTL of 60 seconds.

2. Step 2: Check TTL command output

   The TTL command returns the remaining time to live in seconds. Immediately after setting, it should be 60.

3. Final Answer:

   60 -> Option A

4. Quick Check:

   TTL after SET with EX 60 = 60 [OK]

Hint: TTL shows seconds left, right after SET with EX it's full time [OK]

Common Mistakes:

• Expecting TTL to return -1 (no expiration)
• Confusing -2 (key does not exist) with TTL
• Thinking TTL returns 0 immediately

4. You run the following commands:

SET temp_key "data" EX 30
EXPIRE temp_key 60
TTL temp_key

What will TTL temp_key return?

medium

A. 60

B. 30

C. -1

D. -2

Solution

1. Step 1: SET with EX 30 sets TTL to 30 seconds

   The key temp_key initially has 30 seconds TTL.

2. Step 2: EXPIRE command updates TTL to 60 seconds

   The EXPIRE temp_key 60 resets the TTL to 60 seconds.

3. Step 3: TTL command returns updated TTL

   So, TTL temp_key returns 60 seconds remaining.

4. Final Answer:

   60 -> Option A

5. Quick Check:

   EXPIRE updates TTL, TTL shows new value [OK]

Hint: EXPIRE resets TTL, TTL shows latest expiration [OK]

Common Mistakes:

• Assuming TTL stays at original 30 seconds
• Confusing TTL -1 (no expiration) with updated TTL
• Thinking EXPIRE does not change TTL

5. You want to store a temporary login token in Redis that expires after 5 minutes. Which sequence of commands correctly sets the token and checks its remaining TTL after 3 minutes?

hard

A. SET login_token abc EX 300
SLEEP 180
EXISTS login_token

B. SET login_token abc PX 300
WAIT 180
EXISTS login_token

C. SET login_token abc EX 300
SLEEP 180
TTL login_token

D. SET login_token abc EX 300
WAIT 180
EXISTS login_token

Solution

1. Step 1: Use SET with EX 300 for 5 minutes expiration

   The command SET login_token abc EX 300 sets the token with 300 seconds TTL.

2. Step 2: Wait 180 seconds (3 minutes) and check TTL

   Using SLEEP 180 simulates waiting. Then TTL login_token shows remaining time, confirming token still exists.

3. Step 3: EXISTS only returns 1 or 0, TTL shows time left

   Checking TTL is better to confirm token is still valid and how long it lasts.

4. Final Answer:

   SET login_token abc EX 300 SLEEP 180 TTL login_token -> Option C

5. Quick Check:

   SET with EX + wait + TTL check = correct flow [OK]

Hint: Use SET with EX, wait, then TTL to check remaining time [OK]

Common Mistakes:

• Using PX instead of EX for seconds
• Using WAIT instead of SLEEP (WAIT waits for replicas, not sleep)
• Using EXISTS which only returns existence, not TTL