Redis Commands

These are the commands we are using

• HSET: stores multiple pieces of information under one key, like a mini dictionary. Think of it like a contact card.
  • The key is the person’s name.
  • The fields are labels like “age” or “city”.
  • The values are the actual age or city name.

  

  Redis offers different data structures, SET and HSET commands belong to two different ones:

  • SET works with simple string values.
  • HSET works with hashes (think: mini‑key/value maps stored under one top-level key).
• HGET: retrieves the value of a specific field from a hash stored at a given key in Redis.

  > HSET myhash field1 "foo"
  (integer) 1
  > HGET myhash field1
  "foo"
  > HGET myhash field2
  (nil)
  

• ZADD: Add/update members in a sorted set with a score.

  > ZADD scores 90 "Alice" 85 "Bob" 95 "Charlie"
  (integer) 3
  

  • This creates a sorted set scores with:
    • Alice with score 90.
    • Bob with score 85.
    • Charlie with score 95.
  • The set is sorted by score in ascending order:

    Bob (85), Alice (90), Charlie (95).
    

  > ZADD scores 192 "Alice"
  (integer) 0
  

  • Updates Alice’s score to 192. Meaning alice will take Charlie’s position.
• ZRANGE: retrieves a specified range of elements from a sorted set.
  • It supports three types of range queries:
    • By index (rank):
      • Use 0-based indexes to get elements by position.
      • Negative numbers count from the end.

      > ZRANGE scores 0 -1 WITHSCORES
      1) "Bob"
      2) "85"
      3) "Charlie"
      4) "95"
      5) "Alice"
      6) "192"
      

    • By score:
      • Use BYSCORE to get elements within a score range.
      • You can use -inf and +inf for infinity, and (start, stop) for exclusive ranges.
      • The one used in our OutboxService.
    • By lexicographical order:
      • Use BYLEX to get elements within a string range.
      • Use [ for inclusive and ( for exclusive ranges.
  • Additional options:
    • REV: Reverses the order (highest to lowest score).
    • LIMIT: Limits the number of results returned.
    • WITHSCORES: Returns both values and their scores.
• ZREM: Removes the specified members from the sorted set stored at key. Non existing members are ignored.

  > ZREM scores "Alice"
  (integer) 1
  > ZRANGE scores 0 -1 WITHSCORES
  1) "Bob"
  2) "85"
  3) "Charlie"
  4) "95"
  

• SET: sets a key to a string value (used here with NX and PX for locks).
  • NX option: set only if not exists.
  • PX option: sets the TTL for a key in milliseconds.

    > SET key value PX 5000
    

• DEL: removes the specified keys. A key is ignored if it does not exist.

  > SET key1 "val1"
  "OK"
  > SET key2 "val2"
  "OK"
  > DEL key1 key2 key3
  (integer) 2
  

  This command’s behavior varies in clustered Redis environments. In ioredis we have to delete them individually if they are in different slots.