KEYS pattern matching (avoid in production) in Redis - Mini Project: Build & Apply

Using Redis KEYS Pattern Matching (Avoid in Production)

📖 Scenario: You are managing a Redis database that stores user session data with keys that include user IDs and session info. You want to find all keys related to a specific user quickly.

🎯 Goal: Build a simple Redis command sequence to find all keys matching a pattern for a specific user ID using the KEYS command.

📋 What You'll Learn

Create keys in Redis with exact names: session:1001, session:1002, session:1003, cache:1001, cache:1002

Set a pattern variable called pattern with the value session:100*

Use the KEYS command with the pattern variable to find matching keys

Store the result in a variable called matching_keys

💡 Why This Matters

🌍 Real World

Finding keys by pattern helps in debugging and managing Redis data during development or small projects.

💼 Career

Understanding Redis key pattern matching is useful for roles involving caching, session management, and fast data retrieval.

1

DATA SETUP: Create Redis keys for sessions and cache

Create Redis keys with exact names: session:1001, session:1002, session:1003, cache:1001, and cache:1002. Use the SET command to assign any string value to each key.

Redis

# Your code here

Hint

Use the SET command followed by the key name and a string value.

2

CONFIGURATION: Define the pattern variable

Create a variable called pattern and set it to the string session:100* to match all session keys starting with session:100.

Redis

SET session:1001 "data1"
SET session:1002 "data2"
SET session:1003 "data3"
SET cache:1001 "cache1"
SET cache:1002 "cache2"

# Define the pattern variable
# Your code here

Hint

Assign the pattern string to a variable named pattern.

3

CORE LOGIC: Use KEYS command with the pattern variable

Use the KEYS command with the variable pattern to find all keys matching the pattern. Store the result in a variable called matching_keys.

Redis

SET session:1001 "data1"
SET session:1002 "data2"
SET session:1003 "data3"
SET cache:1001 "cache1"
SET cache:1002 "cache2"

pattern=session:100*

# Use KEYS command with pattern and store in matching_keys
# Your code here

Hint

Use KEYS followed by the pattern string to find matching keys and assign to matching_keys.

4

COMPLETION: Finalize the Redis command sequence

Ensure the Redis commands include setting the keys, defining the pattern variable, and using the KEYS command to assign matching keys to matching_keys.

Redis

SET session:1001 "data1"
SET session:1002 "data2"
SET session:1003 "data3"
SET cache:1001 "cache1"
SET cache:1002 "cache2"

pattern=session:100*

matching_keys=$(redis-cli KEYS "$pattern")

# Finalize your Redis commands here
# Your code here

Hint

Review all previous commands to ensure completeness and correctness.

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