Session storage pattern in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Redis

SET session:user123 [1]

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

A"active"

BEXPIRE

CGET

DDEL

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands like EXPIRE or GET instead of a value.

Forgetting to provide a value after the key.

The SET command stores a key with a value. Here, we set the session key session:user123 to the string "active".

2fill in blank

medium

Complete the code to set an expiration time of 3600 seconds on a session key.

Redis

EXPIRE session:user123 [1]

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

A60

B0

C1800

D3600

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which means no expiration.

Using a time too short or too long by mistake.

The EXPIRE command sets the time to live for a key in seconds. Here, 3600 seconds means the session expires in one hour.

3fill in blank

hard

Fix the error in the command to retrieve the session value.

Redis

[1] session:user123

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

ASET

BEXPIRE

CGET

DDEL

Attempts:

3 left

💡 Hint

Common Mistakes

Using SET instead of GET to retrieve data.

Using EXPIRE or DEL which do not return the value.

The GET command retrieves the value stored at the given key. Using SET or others here would cause errors or wrong behavior.

4fill in blank

hard

Fill both blanks to delete a session key and then check if it still exists.

Redis

DEL [1]
EXISTS [2]

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

Asession:user456

Bsession:user123

Csession:user789

Dsession:user000

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys in DEL and EXISTS commands.

Using keys that were not set before.

We delete the session key session:user123 and then check if it exists. Both commands use the same key.

5fill in blank

hard

Fill all three blanks to set a session key with a value and expiration in one command.

Redis

SET [1] [2] [3] 1800

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

Asession:user789

B"logged_in"

CEX

DNX

Attempts:

3 left

💡 Hint

Common Mistakes

Using NX which means set only if key does not exist, not expiration.

Forgetting to put quotes around the value string.

This command sets the key session:user789 with the value "logged_in" and expiration time of 1800 seconds (30 minutes). The EX option specifies the expiration in seconds.

Practice

1. What is the main purpose of using Redis for session storage?

easy

A. To keep temporary user data during their visit

B. To permanently store user files

C. To perform complex calculations

D. To replace the database for all data

Solution

1. Step 1: Understand session storage concept

   Session storage is used to keep temporary data about a user while they interact with a website or app.

2. Step 2: Identify Redis role in session storage

   Redis is used to store this temporary data quickly and with expiration to remove it after the session ends.

3. Final Answer:

   To keep temporary user data during their visit -> Option A

4. Quick Check:

   Session storage = temporary user data [OK]

Hint: Session storage = temporary user data storage [OK]

Common Mistakes:

• Thinking Redis stores permanent files
• Confusing session storage with database replacement
• Assuming Redis does complex calculations

2. Which Redis command is used to save session data with an expiration time?

easy

A. GET

B. HGETALL

C. DEL

D. SETEX

Solution

1. Step 1: Recall Redis commands for session storage

   GET retrieves data, DEL deletes data, HGETALL gets all hash fields, SETEX sets a key with expiration.

2. Step 2: Identify command to save with expiration

   SETEX is the command that sets a key's value and expiration time in one step.

3. Final Answer:

   SETEX -> Option D

4. Quick Check:

   Save with expiration = SETEX [OK]

Hint: SETEX sets value with expiration in Redis [OK]

Common Mistakes:

• Using GET to save data
• Using DEL to save data
• Confusing HGETALL with setting data

3. Given the commands:
SETEX session:12345 300 "user_data"
GET session:12345
What will be the output of the GET command immediately after SETEX?

medium

A. SyntaxError

B. nil

C. "user_data"

D. 300

Solution

1. Step 1: Understand SETEX effect

   SETEX sets the key 'session:12345' with value 'user_data' and expiration 300 seconds.

2. Step 2: Check GET output immediately after SETEX

   Since the key exists and is not expired yet, GET returns the stored value 'user_data'.

3. Final Answer:

   "user_data" -> Option C

4. Quick Check:

   GET after SETEX returns stored value [OK]

Hint: GET returns value if key exists and not expired [OK]

Common Mistakes:

• Expecting nil immediately after SETEX
• Confusing expiration time with returned value
• Thinking GET returns expiration time

4. What is wrong with this Redis command sequence for session deletion?
DEL session:12345
GET session:12345

medium

A. DEL command syntax is incorrect

B. No error; GET returns nil after DEL

C. GET will still return data after DEL

D. DEL does not delete keys

Solution

1. Step 1: Check DEL command correctness

   DEL session:12345 is correct syntax to delete the key.

2. Step 2: Understand GET after DEL

   After deletion, GET returns nil because the key no longer exists.

3. Final Answer:

   No error; GET returns nil after DEL -> Option B

4. Quick Check:

   DEL deletes key, GET returns nil [OK]

Hint: DEL removes key; GET returns nil after deletion [OK]

Common Mistakes:

• Thinking DEL syntax is wrong
• Expecting GET to return old data after DEL
• Believing DEL does not remove keys

5. You want to store user session data in Redis that expires after 10 minutes. Which sequence correctly sets and later deletes the session?

hard

A. SETEX session:abc 600 "data"; DEL session:abc

B. SET session:abc "data"; DEL session:abc; EXPIRE session:abc 600

C. SET session:abc 600 "data"; EXPIRE session:abc 600; DEL session:abc

D. GET session:abc; SET session:abc 600 "data"; DEL session:abc

Solution

1. Step 1: Identify correct way to set with expiration

   SETEX sets the key with value and expiration in one command, which is efficient and correct.

2. Step 2: Confirm deletion after setting

   DEL removes the key when session ends, so DEL after SETEX is correct.

3. Final Answer:

   SETEX session:abc 600 "data"; DEL session:abc -> Option A

4. Quick Check:

   SETEX sets with expiry, DEL deletes key [OK]

Hint: Use SETEX to set with expiry, then DEL to delete [OK]

Common Mistakes:

• Setting expiration after deleting key
• Using GET before setting session
• Setting expiration separately instead of SETEX