RENAME and RENAMENX in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the RENAME command do in Redis?

The RENAME command changes the name of an existing key to a new name, overwriting the new key if it already exists.

beginner

How does RENAMENX differ from RENAME in Redis?

RENAMENX renames a key only if the new key name does not already exist. If the new key exists, it does nothing and returns 0.

beginner

What happens if you use RENAME on a key that does not exist?

Redis returns an error because the source key must exist to be renamed.

beginner

What is the return value of RENAMENX when the rename is successful?

RENAMENX returns 1 if the key was renamed successfully.

beginner

Can RENAME overwrite an existing key in Redis?

Yes, RENAME will overwrite the destination key if it already exists.

What does the RENAME command do if the new key already exists?

A It merges both keys

B It returns an error

C It does nothing and returns 0

D It overwrites the existing key with the old key's value

RENAME overwrites the destination key if it already exists.

What does RENAMENX return if the new key name already exists?

A 1

B 0

C An error message

D The old key's value

RENAMENX returns 0 and does not rename if the new key exists.

Which command will rename a key only if the new key does not exist?

A RENAMENX

B RENAME

C DEL

D EXISTS

RENAMENX renames only if the new key does not exist.

What happens if you try to RENAME a key that does not exist?

A Redis returns an error

B It returns 0

C The command creates a new key

D It renames to an empty key

RENAME requires the source key to exist; otherwise, it returns an error.

Which command can overwrite an existing key in Redis?

A SETNX

B RENAMENX

C RENAME

D GET

RENAME overwrites the destination key if it exists.

Explain the difference between RENAME and RENAMENX commands in Redis.

Think about what happens when the new key already exists.

Describe what happens when you use RENAME on a key that does not exist.

Consider the requirement for the source key.

Practice

1. What does the Redis command RENAME do?

easy

A. Changes the name of a key and overwrites the new key if it exists

B. Changes the name of a key only if the new key does not exist

C. Deletes a key without renaming

D. Creates a copy of a key with a new name

Solution

1. Step 1: Understand the purpose of RENAME

   The RENAME command changes the name of an existing key to a new name.

2. Step 2: Check behavior when new key exists

   If the new key already exists, RENAME overwrites it without error.

3. Final Answer:

   Changes the name of a key and overwrites the new key if it exists -> Option A

4. Quick Check:

   RENAME overwrites existing keys = B [OK]

Hint: RENAME always renames and overwrites existing keys [OK]

Common Mistakes:

• Thinking RENAME only renames if new key is free
• Confusing RENAME with RENAMENX
• Assuming RENAME copies instead of renaming

2. Which of the following is the correct syntax to rename a key oldkey to newkey using RENAMENX?

easy

A. RENAMENX newkey oldkey

B. RENAME oldkey newkey

C. RENAMENX oldkey newkey

D. RENAMEX oldkey newkey

Solution

1. Step 1: Recall RENAMENX syntax

   The correct syntax is RENAMENX oldkey newkey, where the first argument is the current key and the second is the new key.

2. Step 2: Identify incorrect options

   A reverses arguments, B uses RENAME not RENAMENX, D has a typo in command name.

3. Final Answer:

   RENAMENX oldkey newkey -> Option C

4. Quick Check:

   RENAMENX oldkey newkey syntax = C [OK]

Hint: Remember: RENAMENX oldkey newkey [OK]

Common Mistakes:

• Swapping oldkey and newkey arguments
• Using RENAME instead of RENAMENX
• Typo in command name

3. Given the following Redis commands executed in order:

SET key1 "value1"
SET key2 "value2"
RENAMENX key1 key2
GET key1
GET key2

What will be the output of the two GET commands?

medium

A. GET key1: "value1", GET key2: "value2"

B. GET key1: nil, GET key2: "value1"

C. GET key1: "value1", GET key2: "value1"

D. GET key1: nil, GET key2: "value2"

Solution

1. Step 1: Analyze RENAMENX behavior

   RENAMENX renames key1 to key2 only if key2 does not exist. Here, key2 exists, so RENAMENX does nothing.

2. Step 2: Check GET results

   Since RENAMENX failed, key1 still holds "value1" and key2 holds "value2".

3. Final Answer:

   GET key1: "value1", GET key2: "value2" -> Option A

4. Quick Check:

   RENAMENX fails if new key exists = A [OK]

Hint: RENAMENX fails if new key exists, keys unchanged [OK]

Common Mistakes:

• Assuming RENAMENX overwrites existing keys
• Expecting key1 to be deleted after RENAMENX
• Confusing RENAMENX with RENAME

4. You run the command RENAMENX keyA keyB but get an error saying ERR no such key. What is the most likely cause?

medium

A. keyB does not exist

B. RENAMENX command is misspelled

C. keyB already exists

D. keyA does not exist

Solution

1. Step 1: Understand error meaning

   The error ERR no such key means the source key to rename does not exist.

2. Step 2: Identify which key is source

   In RENAMENX keyA keyB, keyA is the source key. If it does not exist, the error occurs.

3. Final Answer:

   keyA does not exist -> Option D

4. Quick Check:

   ERR no such key means source key missing = D [OK]

Hint: ERR no such key means source key missing [OK]

Common Mistakes:

• Thinking error means destination key missing
• Assuming RENAMENX overwrites keys
• Ignoring command spelling

5. You want to rename a key session123 to user_session only if user_session does not exist, and get a confirmation if rename succeeded. Which Redis command and response should you use?

hard

A. Use RENAME session123 user_session and expect OK response

B. Use RENAMENX session123 user_session and expect 1 if renamed, 0 if not

C. Use RENAMENX user_session session123 and expect 1 if renamed

D. Use RENAME user_session session123 and expect OK response

Solution

1. Step 1: Choose command that renames only if new key is free

   RENAMENX renames only if the new key does not exist, perfect for this case.

2. Step 2: Understand RENAMENX response

   RENAMENX returns 1 if rename succeeded, 0 if new key exists and rename skipped.

3. Final Answer:

   Use RENAMENX session123 user_session and expect 1 if renamed, 0 if not -> Option B

4. Quick Check:

   RENAMENX returns 1 or 0 for success/failure = A [OK]

Hint: RENAMENX returns 1 if renamed, 0 if new key exists [OK]

Common Mistakes:

• Using RENAME which always overwrites
• Swapping source and destination keys
• Expecting OK response from RENAMENX