ZUNION

Returns the union of multiple sorted sets.

Browse all commands · Upstream source documentation

Reference field	Value
Canonical name	ZUNION
Catalog group	Sorted set commands
Upstream since	6.2.0 — upstream Redis/module version, not an ffkv release
Pinned catalog	Redis 8.10.0

Syntax

ZUNION numkeys key [key ...] [WEIGHTS weight [weight ...]]
  [AGGREGATE <SUM | MIN | MAX | COUNT>] [WITHSCORES]

ffkv behavior and limits

Scores and lexicographic ranges are separate query modes. Do not rely on random-pop order; sorted-set storage remains RAM-resident in hybrid mode.

Source: README.md:275–295, 810–825; tests/bdd/features/sorted_sets.feature.

All requests share the 8 MiB framing/1,024-argument ingress limit; normal RESP replies have 64 MiB wire/logical budgets with bounded nesting/value counts. Management and Lua origins impose smaller budgets. These are not a process RSS cap. Catalog inclusion is not exhaustive option or wire-format parity. See limits and compatibility.

Upstream metadata

The following fields come from the pinned Redis metadata, not measured ffkv performance or an assertion that ffkv enforces every upstream flag. Running COMMAND INFO/COMMAND DOCS describe the current engine.

Upstream Redis complexity: O(N)+O(M*log(M)) with N being the sum of the sizes of the input sorted sets, and M being the number of elements in the resulting sorted set.

Upstream arity: -3 (includes the command name; a negative number is a minimum).

Command flags: READONLY.

ACL categories: SORTEDSET.

Argument structure

Argument	Type	Constraints / metadata
numkeys	integer	Required
key	key	multiple; key_spec_index: 0
weight	integer	optional; multiple; token: WEIGHTS
aggregate	oneof	optional; token: AGGREGATE
↳ sum	pure-token	token: SUM
↳ min	pure-token	token: MIN
↳ max	pure-token	token: MAX
↳ count	pure-token	token: COUNT; since: 8.8.0
withscores	pure-token	optional; token: WITHSCORES

Key specifications

Upstream key discovery descriptors (indexes are relative to the full command vector):

[
  {
    "flags": [
      "RO",
      "ACCESS"
    ],
    "begin_search": {
      "index": {
        "pos": 1
      }
    },
    "find_keys": {
      "keynum": {
        "keynumidx": 0,
        "firstkey": 1,
        "step": 1
      }
    }
  }
]

Additional pinned upstream metadata

{
  "group": "sorted_set",
  "since": "6.2.0",
  "history": [
    [
      "8.8.0",
      "Added `COUNT` aggregate option."
    ]
  ]
}

Metadata source · Local snapshot: src/command_metadata.json, key zunion.

BDD coverage and source examples

These are source observations, not a test run performed by this documentation build. A tag identifies scenario intent; an extracted vector identifies a command invocation, which may intentionally produce an error. Scenarios may require setup, multiple connections, persistence, cluster nodes or native-module fixtures.

• Union applies per-input weights before aggregation including regular sets — tests/bdd/features/sorted_sets.feature:641; command tag and invocation observed.
• RESP3 algebra uses scored pairs and weighted COUNT ignores scores — tests/bdd/features/sorted_sets.feature:950; command tag and invocation observed.
• Weight zero normalizes infinity products to zero and MIN differs from SUM — tests/bdd/features/sorted_sets.feature:1102; command tag and invocation observed.
• Only union and intersection accept regular set inputs — tests/bdd/features/sorted_sets.feature:1276; command tag and invocation observed.
• An initial zero-weight infinity product is normalized but union normalizes all contributions — tests/bdd/features/sorted_sets.feature:1357; command tag and invocation observed.

Extracted command vectors

The following JSON arrays are the test harness’s argument vectors, not shell commands. Numeric arguments are converted by the harness; objects of the form {"base64":"…"} represent decoded binary bytes, not a literal JSON command argument. Preserve scenario setup and connection ordering. See the CLI guide for shell quoting and binary stdin. No reply is invented or inferred.

RESP3 algebra uses scored pairs and weighted COUNT ignores scores — tests/bdd/features/sorted_sets.feature:965 (client “reader” executes:)

[
  "ZUNION",
  "1",
  "left",
  "WITHSCORES"
]

Next source assertion: the reply equals:

[["a",1],["b",2],["c",4]]

Only union and intersection accept regular set inputs — tests/bdd/features/sorted_sets.feature:1290 (I execute:)

[
  "ZUNION",
  "1",
  "plain",
  "WITHSCORES"
]

Next source assertion: the reply equals:

["a","1","b","1"]

Weight zero normalizes infinity products to zero and MIN differs from SUM — tests/bdd/features/sorted_sets.feature:1108 (I execute:)

[
  "ZUNION",
  "2",
  "left",
  "right",
  "WEIGHTS",
  "0",
  "1",
  "WITHSCORES"
]

Next source assertion: the reply equals:

["a","2","b","3"]