LPOP

Returns the first elements in a list after removing it. Deletes the list if the last element was popped.

Browse all commands · Upstream source documentation

Reference field	Value
Canonical name	LPOP
Catalog group	List commands
Upstream since	1.0.0 — upstream Redis/module version, not an ffkv release
Pinned catalog	Redis 8.10.0

Syntax

LPOP key [count]

ffkv behavior and limits

A successful pop removes the item immediately: Redis list queues have no acknowledgement or automatic redelivery. Blocking calls do not wait in EXEC or Lua. Only large list/native-job bodies are SSD-offloaded in hybrid mode.

Source: README.md:155–174, 810–825; tests/bdd/features/lists.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) where N is the number of elements returned

Upstream arity: -2 (includes the command name; a negative number is a minimum).

Command flags: WRITE, FAST.

ACL categories: LIST.

Argument structure

Argument	Type	Constraints / metadata
key	key	key_spec_index: 0
count	integer	optional; since: 6.2.0

Key specifications

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

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

Additional pinned upstream metadata

{
  "group": "list",
  "since": "1.0.0",
  "history": [
    [
      "6.2.0",
      "Added the `count` argument."
    ]
  ]
}

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

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.

• Unblock completes a real list waiter with timeout semantics and does not consume later data — tests/bdd/features/connections.feature:353; invocation observed.
• Counted pops return traversal order and delete emptied keys — tests/bdd/features/lists.feature:93; command tag and invocation observed.
• Zero counts do not consume and negative counts fail atomically (Scenario Outline) — tests/bdd/features/lists.feature:130; command tag and invocation observed.
• List commands reject incompatible source values without replacing them (Scenario Outline) — tests/bdd/features/lists.feature:1047; 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.

Counted pops return traversal order and delete emptied keys — tests/bdd/features/lists.feature:123 (I execute:)

[
  "LPOP",
  "q"
]

Next source assertion: the reply is null

Zero counts do not consume and negative counts fail atomically — tests/bdd/features/lists.feature:136 (I execute:)

Expanded from an actual Examples row: command=LPOP.

[
  "LPOP",
  "q",
  "0"
]

Next source assertion: the reply equals:

[]

Unblock completes a real list waiter with timeout semantics and does not consume later data — tests/bdd/features/connections.feature:389 (client “waiting” executes:)

[
  "LPOP",
  "empty-list"
]

Next source assertion: the reply equals:

"retained"