LCS

Finds the longest common substring.

Browse all commands · Upstream source documentation

Reference field	Value
Canonical name	LCS
Catalog group	String commands
Upstream since	7.0.0 — upstream Redis/module version, not an ffkv release
Pinned catalog	Redis 8.10.0

Syntax

LCS key1 key2 [LEN] [IDX] [MINMATCHLEN min-match-len] [WITHMATCHLEN]

ffkv behavior and limits

Keys and values are binary-safe bytes. Conditional SET and DELEX comparisons use the stored bytes; DIGEST uses XXH3, not a cryptographic digest.

Source: README.md:571–585; src/engine/strings.rs; tests/bdd/features/strings.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*M) where N and M are the lengths of s1 and s2, respectively

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

Command flags: READONLY.

ACL categories: STRING.

Argument structure

Argument	Type	Constraints / metadata
key1	key	key_spec_index: 0
key2	key	key_spec_index: 0
len	pure-token	optional; token: LEN
idx	pure-token	optional; token: IDX
min-match-len	integer	optional; token: MINMATCHLEN
withmatchlen	pure-token	optional; token: WITHMATCHLEN

Key specifications

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

[
  {
    "flags": [
      "RO",
      "ACCESS"
    ],
    "begin_search": {
      "index": {
        "pos": 1
      }
    },
    "find_keys": {
      "range": {
        "lastkey": 1,
        "step": 1,
        "limit": 0
      }
    }
  }
]

Additional pinned upstream metadata

{
  "group": "string",
  "since": "7.0.0"
}

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

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.

• Longest subsequence is not restricted to contiguous bytes — tests/bdd/features/strings.feature:580; command tag and invocation observed.
• String type errors never destroy a collection (Scenario Outline) — tests/bdd/features/strings.feature:1139; 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.

Longest subsequence is not restricted to contiguous bytes — tests/bdd/features/strings.feature:586 (I execute:)

[
  "LCS",
  "a",
  "b"
]

Next source assertion: the reply equals:

"mytext"

String type errors never destroy a collection — tests/bdd/features/strings.feature:1145 (I execute:)

Expanded from an actual Examples row: argv=["LCS","typed","missing"], code=WRONGTYPE.

[
  "LCS",
  "typed",
  "missing"
]

Next source assertion: the reply is an error with code “WRONGTYPE”

Longest subsequence is not restricted to contiguous bytes — tests/bdd/features/strings.feature:594 (I execute:)

[
  "LCS",
  "a",
  "b",
  "LEN"
]

Next source assertion: the reply equals:

6