# PFMERGE

```json metadata
{
  "title": "PFMERGE",
  "description": "Merges one or more HyperLogLog values into a single key.",
  "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"],
  "arguments": [{"display_text":"destkey","key_spec_index":0,"name":"destkey","type":"key"},{"display_text":"sourcekey","key_spec_index":1,"multiple":true,"name":"sourcekey","optional":true,"type":"key"}],
  "syntax_fmt": "PFMERGE destkey [sourcekey [sourcekey ...]]",
  "complexity": "O(N) to merge N HyperLogLogs, but with high constant times.",
  "group": "hyperloglog",
  "command_flags": ["write","denyoom"],
  "acl_categories": ["@write","@hyperloglog","@slow"],
  "since": "2.8.9",
  "arity": -2,
  "key_specs": [{"RW":true,"access":true,"begin_search":{"spec":{"index":1},"type":"index"},"find_keys":{"spec":{"keystep":1,"lastkey":0,"limit":0},"type":"range"},"insert":true},{"RO":true,"access":true,"begin_search":{"spec":{"index":2},"type":"index"},"find_keys":{"spec":{"keystep":1,"lastkey":-1,"limit":0},"type":"range"}}],
  "tableOfContents": {"sections":[{"id":"examples","title":"Examples"},{"id":"redis-enterprise-and-redis-cloud-compatibility","title":"Redis Enterprise and Redis Cloud compatibility"},{"id":"return-information","title":"Return information"}]}
}
```













Merge multiple HyperLogLog values into a unique value that will approximate
the cardinality of the union of the observed Sets of the source HyperLogLog
structures.

The computed merged HyperLogLog is set to the destination variable, which is
created if does not exist (defaulting to an empty HyperLogLog).

If the destination variable exists, it is treated as one of the source sets 
and its cardinality will be included in the cardinality of the computed
HyperLogLog.

## Examples


PFADD hll1 foo bar zap a
PFADD hll2 a b c foo
PFMERGE hll3 hll1 hll2
PFCOUNT hll3


## Redis Enterprise and Redis Cloud compatibility

| Redis<br />Enterprise | Redis<br />Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> |
|:----------------------|:-----------------|:------|
| <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> |  |

## Return information

{{< multitabs id="pfmerge-return-info" 
    tab1="RESP2" 
    tab2="RESP3" >}}

[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK`.

-tab-sep-

[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK`.