Redis Change En

Redis Modifications (Additional Commands)

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SLOTSINFO [start] [count]

• Description: Returns slot metadata in Redis, including slot ID and key count for each slot.

• Parameters: Defaults to querying [0, MAX_SLOT_NUM).

  • start: starting slot ID (default 0)
  • count: size of the range to query, i.e. [start, start + count) (default MAX_SLOT_NUM)

• Return: an array of slotinfo items, where each slotinfo is [slotnum, slotsize].

  Copy

    response := []slotinfo{slot1, slot2, slot3, ...}
    slotinfo := []int{slotnum, slotsize}
  
    where:
        INT slotnum  : slot ID
        INT slotsize : number of keys in the slot
  

• Example:

  Copy

    localhost:6379> slotsinfo 0 128
        1) 1) (integer) 23
           2) (integer) 2
        2) 1) (integer) 29
           2) (integer) 1
  

SLOTSSCAN slotnum cursor [COUNT count]

• Description: Scans keys in a specific slot.

• Parameters: Similar to SCAN.

  • slotnum: slot ID to scan, in [0, MAX_SLOT_NUM)
  • cursor: same semantics as SCAN
  • [COUNT count]: same semantics as SCAN
    • MATCH is currently not supported

• Return: same format as SCAN.

  • Returns updated cursor and a key list.

• Example:

  Copy

    localhost:6379> slotsscan 579 0 COUNT 10
        1) "10752"
        2)  1) "{a}7836"
            2) "{a}2167"
            3) "{a}5332"
            4) "{a}6292"
            5) "{a}600"
            6) "{a}6094"
            7) "{a}7754"
            8) "{a}4929"
            9) "{a}9211"
           10) "{a}6596"
  

SLOTSDEL slot1 [slot2 …]

• Description: Deletes all key-value pairs in one or more slots.

• Parameters: Accepts at least one slot ID.

• Return: Same structure as slotsinfo; slotsize means remaining keys after deletion (usually 0).

• Example:

  Copy

    localhost:6379> slotsdel 1013 990
        1) 1) (integer) 1013
           2) (integer) 0
        2) 1) (integer) 990
           2) (integer) 0
  

Data Migration

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The following 4 commands are a migration family:

• SLOTSMGRTSLOT - O(1)

  Randomly migrates one key-value pair from a slot to the target node.

• SLOTSMGRTONE - O(1)

  Migrates the specified key-value pair to the target node.

• SLOTSMGRTTAGSLOT - O(log(n))

  Randomly picks one key from a slot and migrates all key-value pairs with the same tag.

• SLOTSMGRTTAGONE - O(log(n))

  Migrates all key-value pairs that share the same tag as the specified key.

SLOTSMGRTSLOT host port timeout slot

• Description: Randomly migrates one key-value pair from the specified slot to the target node (synchronous I/O).

  • Returns 0 if the slot is empty or the selected key expired.
  • If the slot still has keys, one key is selected and migrated.
  • Also returns the remaining key count in the slot.
  • Migration triggers slotsrestore on the destination and overwrites existing values.

• Parameters:

  • host:port: destination node

    Redis caches the connection to host:port for 30s, and closes it on timeout/error.

  • timeout: timeout in milliseconds

    The operation includes three synchronous stages:

    1. connect (may use cached connection)
    2. send key-value data
    3. receive response from destination

    Each stage is bounded by timeout.

  • slot: slot ID to migrate from

• Return: integer array

  Copy

    response := []int{succ,size}
  
    where:
        INT succ : migration result
            0 -> slot is empty (migrated keys = 0)
            1 -> one key migrated and removed locally (migrated keys = 1)
        INT size : remaining key count in the slot
  

• Example:

  Copy

    localhost:6379> set a 100            # set <a, 100>
        OK
    localhost:6379> slotsinfo            # slot size = 1
        1) 1) (integer) 579
           2) (integer) 1
    localhost:6379> slotsmgrt 127.0.0.1 6380 100 579
        (integer) 1                      # migrated successfully
    localhost:6379> slotsinfo
        (empty list or set)
    localhost:6379> slotsmgrt 127.0.0.1 6380 100 579 1
        (integer) 0                      # migrated count = 0; slot already empty
  

SLOTSMGRTONE host port timeout key

• Description: Migrates the specified key to the destination. Semantics are similar to slotsmgrtslot.

• Parameters: see slotsmgrtslot.

• Return: integer

  Copy

    response := int(succ)
  
    where:
        INT succ : same semantics as `slotsmgrtslot`
  

• Example:

  Copy

    localhost:6379> set a 100            # set <a, 100>
        OK
    localhost:6379> slotsinfo
        1) 1) (integer) 579
           2) (integer) 1
    localhost:6379> slotsmgrtone 127.0.0.1 6380 100 a
        (integer) 1                      # migration succeeded
    localhost:6379> slotsmgrtone 127.0.0.1 6380 100 a
        (integer) 0                      # skipped: key does not exist locally
  

SLOTSMGRTTAGONE host port timeout key

• Description: Migrates all keys that share the same tag as key.

  • If key has no valid tag, it degrades to slotsmgrtone, with complexity O(1).
  • If key has a valid tag, it hashes the tag and finds all matching keys in skiplist, then migrates them atomically, with complexity O(log(n)).
  • Note: In the modified Redis, tagged keys are organized in a skiplist by tag hash. Migration by tag may include more keys with the same hash. This design reduces string comparisons during tag migration and improves performance.

• Parameters: see slotsmgrtone.

• Return: integer

  Copy

    response := int(succ)
  
    where:
        INT succ : number of keys migrated successfully
  

• Example:

  Copy

    localhost:6379> set a{tag} 100        # set <a{tag}, 100>
        OK
    localhost:6379> set b{tag} 100        # set <b{tag}, 100>
        OK
    localhost:6379> slotsmgrttag 127.0.0.1 6380 1000 {tag}
        (integer) 2
    localhost:6379> scan 0                # migrated, no local data
        1) "0"
        2) (empty list or set)
    localhost:6380> scan 0                # data appears on destination
        1) "0"
        2) 1) "a{tag}"
           2) "b{tag}"
  

SLOTSMGRTTAGSLOT host port timeout slot

• Description: Tag-based migration counterpart of slotsmgrtslot.

  • Refer to slotsmgrtslot and slotsmgrttagone for behavior details.

SLOTSRESTORE key1 ttl1 val1 [key2 ttl2 val2 …]

• Description: Extension of Redis 2.8 restore command.

  • Supports restoring multiple key-value pairs at once.
  • The operation is atomic.

• Note: Unlike restore, slotsrestore only supports replace, i.e. it always overwrites old values. If old values already exist, it is usually a bug in redis-slots or proxy implementation, and Redis logs a conflict record.

Debug Commands

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SLOTSHASHKEY key1 [key2 …]

• Description: Computes and returns slot IDs of input keys.

• Parameters: one or more keys.

• Return: array

  Copy

    response := []int{slot1, slot2...}
  
    where:
        INT slot : slot ID of the key, i.e. hash32(key) % NUM_OF_SLOTS
  

• Example:

  Copy

    localhost:6379> slotshashkey a b c   # compute slot IDs of <a,b,c>
        1) (integer) 579
        2) (integer) 1017
        3) (integer) 879
  

SLOTSCHECK

• Description: Performs slot consistency checking in Redis. It verifies:

  • Every key recorded in a slot exists in DB.
  • Every DB key can be found in its corresponding slot.

• Parameters: no arguments.

• Return: string OK on success (or ERR with related key when check fails).

• Example:

  Copy

    localhost:6379> set a 100            # set <a, 100>
        OK
    localhost:6379> slotscheck
        OK                               # check passed
    …
    localhost:6379> slotscheck
        OK                               # check passed, took 1.07s
        (1.07s)
  

• Note: This operation is relatively slow and should be used only as a development/debugging tool, not in production.