Redis - Client

Redis Client

Difference between redis-cli scan, redis-cli --scan, and redis-cli keys:

Command	redis-cli keys	redis-cli scan	redis-cli --scan
Function	Fetches all keys matching a pattern	Iteratively scans keys in batches	Shortcut for SCAN to list all keys
Blocking/Non-Blocking	Blocking (can affect Redis performance)	Non-blocking (safe for production)	Non-blocking (safe for production)
Performance	Slow on large datasets	Fast and efficient for large datasets	Fast and efficient for large datasets
Use Case	Small datasets or quick lookups	Large datasets, production-safe	Large datasets, user-friendly
Cursor Handling	Not applicable	You need to manually manage the cursor	Cursor handled automatically
Pattern Matching	Supports patterns	Supports patterns	Supports patterns

Redis Patterns Use Glob-Style Matching, Not Regular Expressions

• The -scan command with -pattern uses glob-style pattern matching, which is simpler than regular expressions.
• Redis expects patterns with wildcards like:
  • ?: Matches a single character.
  • ``: Matches zero or more characters.
  • [abc]: Matches any character within the brackets.

Example of Valid Patterns:

• "key*": Matches all keys starting with “key”.
• "??abc": Matches keys with exactly 2 characters before “abc”.
• "user[0-9]*": Matches keys starting with “user” followed by a number.

If Regex is Necessary

• Redis itself doesn’t support regex for SCAN. However, you can filter results using external tools like grep or use scripting (e.g., in Python).

• Example using grep to filter keys matching the regex:

    redis-cli --scan | grep -P '^([a-zA-Z0-9]){7}$'
  

Explanation:

• redis-cli --scan: Retrieves keys from Redis.
• grep -E '^([a-zA-Z0-9]){7}$': Filters results to match the regex.

redis-cli --scan examples

1. Populate some keys

    127.0.0.1:6379> debug populate 10 user:id
    OK
    127.0.0.1:6379> keys *
     1) "user:id:6"
     2) "user:id:7"
     3) "user:id:2"
     4) "user:id:3"
     5) "user:id:0"
     6) "user:id:5"
     7) "user:id:9"
     8) "user:id:8"
     9) "user:id:4"
    10) "user:id:1"
    127.0.0.1:6379> debug populate 10 employee:id
    OK
    127.0.0.1:6379> keys *
     1) "user:id:6"
     2) "user:id:7"
     3) "user:id:2"
     4) "employee:id:9"
     5) "employee:id:8"
     6) "user:id:3"
     7) "user:id:0"
     8) "employee:id:5"
     9) "user:id:5"
    10) "employee:id:4"
    11) "user:id:9"
    12) "employee:id:0"
    13) "user:id:8"
    14) "employee:id:1"
    15) "employee:id:3"
    16) "employee:id:7"
    17) "employee:id:2"
    18) "user:id:1"
    19) "user:id:4"
    20) "employee:id:6"
    127.0.0.1:6379> quit
   

2. Bulk delete keys using pipe based on pattern

    ❯ redis-cli --scan --pattern "employee:id*" | awk '{print "UNLINK " $0}' | redis-cli --pipe
    All data transferred. Waiting for the last reply...
    Last reply received from server.
    errors: 0, replies: 10
   

3. Bulk get keys

    ❯ for key in $(redis-cli --scan --pattern "user:id*"); do
      echo "${key} $(redis-cli GET ${key})"
    done
       
    user:id:6 value:6
    user:id:3 value:3
    user:id:8 value:8
    user:id:1 value:1
    user:id:4 value:4
    user:id:7 value:7
    user:id:0 value:0
    user:id:2 value:2
    user:id:9 value:9
    user:id:5 value:5