KEYS pattern matching (avoid in production) in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find all keys starting with 'user:'.

Redis

KEYS [1]

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

Auser:*

Buser?

C*user

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'user?' matches only keys with exactly one character after 'user'.

Using '*user' matches keys ending with 'user', not starting with it.

Using 'user' matches only the exact key 'user'.

The pattern user:* matches all keys that start with 'user:'.

2fill in blank

medium

Complete the code to find all keys that have exactly 5 characters.

Redis

KEYS [1]

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

A?????

B*

C????

D??????

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' matches any length, not exactly 5 characters.

Using fewer or more ? will match keys of wrong length.

The pattern ????? matches keys with exactly 5 characters, each ? matches one character.

3fill in blank

hard

Fix the error in the code to find keys ending with ':id'.

Redis

KEYS [1]

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

A*id:

B*:id

C:id*

Did:*

Attempts:

3 left

💡 Hint

Common Mistakes

Using ':id*' matches keys starting with ':id', not ending.

Using '*id:' or 'id:*' do not match keys ending with ':id'.

The pattern *:id matches keys that end with ':id'.

4fill in blank

hard

Fill both blanks to find keys that start with 'session:' and have exactly 8 characters after the colon.

Redis

KEYS [1][2]

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

Asession:

Buser:

C????????

D???????

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'user:' instead of 'session:' will match wrong keys.

Using 7 question marks matches 7 characters, not 8.

The pattern session:???????? matches keys starting with 'session:' followed by exactly 8 characters.

5fill in blank

hard

Fill all three blanks to find keys that contain 'cache' anywhere and end with a digit.

Redis

KEYS [1][2][3]

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

A*cache*

B*

C[0-9]

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cache' alone matches only keys exactly equal to 'cache'.

Using '*cache*' without [0-9] does not ensure the key ends with a digit.

Using '[0-9]' alone does not match keys containing 'cache'.

The pattern *cache*[0-9] matches keys containing 'cache' anywhere and ending with a digit.

Practice

1. What does the Redis command KEYS * do?

easy

A. Returns all keys in the current database

B. Deletes all keys in the current database

C. Returns the number of keys in the current database

D. Sets a new key with a wildcard name

Solution

1. Step 1: Understand the KEYS command

   The KEYS command searches for keys matching a given pattern.

2. Step 2: Analyze the pattern *

   The pattern * matches all keys in the current database.

3. Final Answer:

   Returns all keys in the current database -> Option A

4. Quick Check:

   KEYS * lists all keys [OK]

Hint: Remember * matches everything in KEYS command [OK]

Common Mistakes:

• Thinking KEYS deletes keys
• Confusing KEYS with COUNT commands
• Assuming KEYS sets keys

2. Which of the following is the correct unquoted syntax to find keys starting with 'user:' using KEYS?

easy

A. KEYS user:*

B. KEYS user*

C. KEYS 'user:*'

D. KEYS 'user*'

Solution

1. Step 1: Understand pattern syntax in KEYS

   Patterns do not require quotes; wildcards like * match any characters.

2. Step 2: Match keys starting with 'user:'

   The pattern should be user:* without quotes to match keys starting with 'user:'.

3. Final Answer:

   KEYS user:* -> Option A

4. Quick Check:

   Use unquoted patterns with * wildcard [OK]

Hint: Use unquoted patterns with * for KEYS [OK]

Common Mistakes:

• Adding quotes around pattern
• Using colon without wildcard
• Using wrong wildcard placement

3. Given keys: user:1, user:2, admin:1, what is the output of KEYS user:*?

medium

A. ["admin:1"]

B. ["user:1", "user:2", "admin:1"]

C. ["user:1", "user:2"]

D. []

Solution

1. Step 1: Identify keys matching pattern user:*

   Keys starting with 'user:' are user:1 and user:2.

2. Step 2: Exclude keys not matching pattern

   admin:1 does not start with 'user:', so it is excluded.

3. Final Answer:

   ["user:1", "user:2"] -> Option C

4. Quick Check:

   Pattern matches keys starting with 'user:' [OK]

Hint: Match only keys starting with pattern prefix [OK]

Common Mistakes:

• Including keys with different prefixes
• Returning empty list incorrectly
• Confusing pattern syntax

4. What is wrong with this command: KEYS user?*?

medium

A. The question mark is not a valid wildcard in KEYS

B. The pattern should be quoted

C. The command will delete keys instead of listing

D. The pattern matches only keys with exactly one character after 'user' followed by any characters

Solution

1. Step 1: Understand the question mark wildcard in KEYS

   The question mark ? matches exactly one character in Redis patterns.

2. Step 2: Analyze the pattern user?*

   This pattern matches keys starting with 'user', followed by exactly one character, then any characters.

3. Final Answer:

   The pattern matches only keys with exactly one character after 'user' -> Option D

4. Quick Check:

   ? matches exactly one character [OK]

Hint: Remember ? matches exactly one character in KEYS [OK]

Common Mistakes:

• Thinking ? is invalid wildcard
• Assuming pattern deletes keys
• Forgetting ? matches exactly one character

5. You want to find all keys containing the word 'session' anywhere in their name without blocking Redis in production. Which approach is best?

hard

A. Use KEYS *session* command directly

B. Use SCAN 0 MATCH *session* iteratively

C. Use GET *session* command

D. Use DEL *session* to remove keys first

Solution

1. Step 1: Understand why KEYS is discouraged in production

   KEYS blocks Redis and can cause performance issues on large datasets.

2. Step 2: Use SCAN with MATCH for safe iteration

   SCAN iterates keys incrementally without blocking, using MATCH *session* to filter keys containing 'session'.

3. Final Answer:

   Use SCAN 0 MATCH *session* iteratively -> Option B

4. Quick Check:

   SCAN is safe for production key matching [OK]

Hint: Use SCAN with MATCH to avoid blocking Redis [OK]

Common Mistakes:

• Using KEYS in production causing blocking
• Using GET with wildcards (invalid)
• Deleting keys without checking