RENAME and RENAMENX in Redis - Step-by-Step Execution

Concept Flow - RENAME and RENAMENX

Start

↓

Check if source key exists

Yes↓

For RENAME:

↓

Rename key, overwrite if target exists

↓

Return OK

↓

End

↓

For RENAMENX:

↓

Check if target key exists

No↓

Rename key

↓

Return 1

↓

End

↓

If target exists in RENAMENX

↓

Do not rename

↓

Return 0

↓

End

The flow checks if the source key exists, then for RENAME it renames and overwrites target if exists, while RENAMENX renames only if target does not exist.

Execution Sample

Redis

SET key1 "Hello"
SET key2 "World"
RENAME key1 key2
RENAMENX key2 key3

This sequence sets two keys, renames key1 to key2 (overwriting key2), then tries to rename key2 to key3 only if key3 does not exist.

Execution Table

Step	Command	Source Key Exists?	Target Key Exists?	Action	Result	State Change
1	SET key1 "Hello"	N/A	N/A	Set key1	OK	key1 = "Hello"
2	SET key2 "World"	N/A	N/A	Set key2	OK	key2 = "World"
3	RENAME key1 key2	Yes	Yes	Rename key1 to key2, overwrite key2	OK	key2 = "Hello", key1 deleted
4	RENAMENX key2 key3	Yes	No	Rename key2 to key3	1	key3 = "Hello", key2 deleted

💡 Commands complete; RENAMENX skips rename if target exists, RENAME always renames and overwrites.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
key1	null	"Hello"	"Hello"	deleted	deleted
key2	null	null	"World"	"Hello"	deleted
key3	null	null	null	null	"Hello"

Key Moments - 2 Insights

Why does RENAME overwrite the target key but RENAMENX does not?

RENAME always renames the source key to the target key, deleting the target if it exists (see step 3 in execution_table). RENAMENX only renames if the target key does not exist, otherwise it does nothing and returns 0 (see step 4).

What happens to the source key after a successful rename?

After renaming, the source key is deleted and no longer exists in the database (see variable_tracker after step 3 and 4).

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is the value of key2 after RENAME key1 key2?

A "World"

B "Hello"

C null

D "key1"

💡 Hint

Check the 'State Change' column at step 3 in execution_table.

At which step does the source key get deleted?

A After step 3

B After step 1

C After step 2

D After step 4

💡 Hint

Look at variable_tracker for key1 after step 3.

If key3 already existed before step 4, what would RENAMENX return?

A 1

B OK

C 0

D Error

💡 Hint

Refer to the concept_flow and execution_table logic for RENAMENX behavior.

Concept Snapshot

RENAME sourceKey targetKey
- Renames sourceKey to targetKey
- Overwrites targetKey if exists
- Returns OK

RENAMENX sourceKey targetKey
- Renames only if targetKey does NOT exist
- Returns 1 if renamed, 0 if not
- Source key deleted after rename

Full Transcript

This visual execution trace shows how Redis commands RENAME and RENAMENX work. First, keys are set with values. RENAME renames a source key to a target key, overwriting the target if it exists, and deletes the source key. RENAMENX renames only if the target key does not exist, otherwise it does nothing. The variable tracker shows key values after each step. Key moments clarify why RENAME overwrites but RENAMENX does not, and what happens to the source key after renaming. The quiz tests understanding of key states and command results.

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