{
  "schema_version": 2,
  "id": "commands/pfmerge",
  "title": "PFMERGE",
  "url": "https://redis.io/docs/latest/commands/pfmerge/",
  "summary": "Merges one or more HyperLogLog values into a single key.",
  "since": "2.8.9",
  "tags": [
    "docs",
    "develop",
    "stack",
    "oss",
    "rs",
    "rc",
    "oss",
    "kubernetes",
    "clients"
  ],
  "last_updated": "2026-09-18T09:48:43+01:00",
  "page_type": "content",
  "content_hash": "ceaf7d6d2b6ba069d5f98af47123e7ece59f808f757e1846775758d7e70e08d2",
  "sections": [
    {
      "id": "overview",
      "title": "Overview",
      "role": "overview",
      "text": "> [!NOTE]\n> This command's behavior varies in clustered Redis environments. See the [multi-key operations](https://redis.io/docs/latest/develop/using-commands/multi-key-operations) page for more information.\n\n\nMerge multiple HyperLogLog values into a unique value that will approximate\nthe cardinality of the union of the observed sets of the source HyperLogLog\nstructures.\n\nThe computed merged HyperLogLog is set to the destination variable, which is\ncreated if it does not exist (defaulting to an empty HyperLogLog).\n\nIf the destination variable exists, it is treated as one of the source sets \nand its cardinality will be included in the cardinality of the computed\nHyperLogLog."
    },
    {
      "id": "required-arguments",
      "title": "Required arguments",
      "role": "content",
      "text": "<details open><summary><code>destkey</code></summary>\n\nThe destination HyperLogLog key in which to store the merged result.\n\n</details>"
    },
    {
      "id": "optional-arguments",
      "title": "Optional arguments",
      "role": "parameters",
      "text": "<details open><summary><code>sourcekey [sourcekey ...]</code></summary>\n\nOne or more source HyperLogLog keys to merge into `destkey`. `destkey` itself is also included in the merge.\n\n</details>"
    },
    {
      "id": "examples",
      "title": "Examples",
      "role": "example",
      "text": "redis> PFADD hll1 foo bar zap a\n(integer) 1\nredis> PFADD hll2 a b c foo\n(integer) 1\nredis> PFMERGE hll3 hll1 hll2\nOK\nredis> PFCOUNT hll3\n(integer) 6"
    },
    {
      "id": "redis-software-and-redis-cloud-compatibility",
      "title": "Redis Software and Redis Cloud compatibility",
      "role": "content",
      "text": "| Redis<br />Software | Redis<br />Cloud | <span style=\"min-width: 9em; display: table-cell\">Notes</span> |\n|:----------------------|:-----------------|:------|\n| <span title=\"Supported\">&#x2705; Standard</span><br /><span title=\"Supported\"><nobr>&#x2705; Active-Active</nobr></span> | <span title=\"Supported\">&#x2705; Standard</span><br /><span title=\"Supported\"><nobr>&#x2705; Active-Active</nobr></span> |  |"
    },
    {
      "id": "return-information",
      "title": "Return information",
      "role": "returns",
      "text": "**RESP2:**\n\n[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK`.\n\n**RESP3:**\n\n[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK`."
    }
  ],
  "examples": []
}