memcached (meta)

The meta protocol is the modern memcached interface, introduced in 1.6. It collapses the classic set / add / replace / append / prepend / cas / get / gets / delete / incr / decr / touch / gat / gats commands into six generic commands governed by single-letter flags:

Command	Purpose
mg	Meta get
ms	Meta set (with payload on next line)
md	Meta delete
ma	Meta arithmetic (incr / decr)
me	Meta debug (dump metadata)
mn	Meta no-op (pipeline barrier)

Framing

Meta commands are line-based like the classic text protocol. ms is the only one with a payload — the value bytes follow the command line on a separate line.

ms greeting 5 T60\r\n
hello\r\n
< HD\r\n

Flags

Each flag is a single ASCII letter, optionally followed immediately by a token. Tokens are alphanumeric, except for M=<mode> which uses an = separator.

mg foo c k v O12345\r\n

Above: c (return CAS), k (echo key), v (return value), O12345 (opaque id).

See Meta flags reference for the canonical table covering all flags across all meta commands.

Responses

Token	Meaning
HD	Header-only success
VA	Value response (header + size + value)
EN	Miss (no entry)
NS	Not stored (precondition failed)
NF	Not found (no entry)
EX	Exists / CAS mismatch
ME	me metadata dump
MN	mn no-op reply

Response flags (appended after the two-letter token) include c, f, s, t, k, O, l, h, and X (stale marker).

Pipelining

mn is the canonical sync barrier. A client batches commands followed by an mn; the MN\r\n reply confirms every preceding command has been processed.

Mixing with classic text

Meta and classic commands share a single connection. A client may issue mg, set, mg, delete, ma on the same socket in any order.