Network Working Group Stone, Ed.
Internet-Draft Six Apart, Ltd.
Intended status: Informational Norbye, Ed.
Expires: March 1, 2009 Sun Microsystems, INC
August 28, 2008
Memcache Binary Protocol
draft-stone-memcache-binary-01
Status of this Memo
This document is an Internet-Draft and is NOT offered in accordance
with Section 10 of RFC 2026, and the author does not provide the IETF
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Abstract
This memo explains the memcache binary protocol for informational
purposes.
Memcache is a high performance key-value cache. It is intentionally
a dumb cache, optimized for speed only. Applications using memcache
do not rely on it for data -- a persistent database with guaranteed
reliability is strongly recommended -- but applications can run much
faster when cached data is available in memcache.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used In This Document . . . . . . . . . . . . 3
2. Packet Structure . . . . . . . . . . . . . . . . . . . . . . . 3
3. Defined Values . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Magic Byte . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Response Status . . . . . . . . . . . . . . . . . . . . . 5
3.3. Command Opcodes . . . . . . . . . . . . . . . . . . . . . 6
3.4. Data Types . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Example . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Get, Get Quietly, Get Key, Get Key Quietly . . . . . . . . 8
4.2.1. Example . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Set, Add, Replace . . . . . . . . . . . . . . . . . . . . 13
4.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 13
4.4. Delete . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.4.1. Example . . . . . . . . . . . . . . . . . . . . . . . 16
4.5. Increment, Decrement . . . . . . . . . . . . . . . . . . . 17
4.5.1. Example . . . . . . . . . . . . . . . . . . . . . . . 18
4.6. quit . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.6.1. Example . . . . . . . . . . . . . . . . . . . . . . . 21
4.7. Flush . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.7.1. Example . . . . . . . . . . . . . . . . . . . . . . . 22
4.8. noop . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.8.1. Example . . . . . . . . . . . . . . . . . . . . . . . 24
4.9. version . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.9.1. Example . . . . . . . . . . . . . . . . . . . . . . . 25
4.10. Append, Prepend . . . . . . . . . . . . . . . . . . . . . 26
4.10.1. Example . . . . . . . . . . . . . . . . . . . . . . . 27
4.11. Stat . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.11.1. Example . . . . . . . . . . . . . . . . . . . . . . . 28
5. Security Considerations . . . . . . . . . . . . . . . . . . . 30
6. Normative References . . . . . . . . . . . . . . . . . . . . . 31
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
Memcache is a high performance key-value cache. It is intentionally
a dumb cache, optimized for speed only. Applications using memcache
should not rely on it for data -- a persistent database with
guaranteed reliability is strongly recommended -- but applications
can run much faster when cached data is available in memcache.
Memcache was originally written to make LiveJournal [LJ] faster. It
now powers all of the fastest web sites that you love.
1.1. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
2. Packet Structure
General format of a packet:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0/ HEADER /
/ /
/ /
/ /
+---------------+---------------+---------------+---------------+
24/ COMMAND-SPECIFIC EXTRAS (as needed) /
+/ (note length in the extras length header field) /
+---------------+---------------+---------------+---------------+
m/ Key (as needed) /
+/ (note length in key length header field) /
+---------------+---------------+---------------+---------------+
n/ Value (as needed) /
+/ (note length is total body length header field, minus /
+/ sum of the extras and key length body fields) /
+---------------+---------------+---------------+---------------+
Total 24 bytes
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Request header:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Magic | Opcode | Key length |
+---------------+---------------+---------------+---------------+
4| Extras length | Data type | Reserved |
+---------------+---------------+---------------+---------------+
8| Total body length |
+---------------+---------------+---------------+---------------+
12| Opaque |
+---------------+---------------+---------------+---------------+
16| CAS |
| |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Response header:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Magic | Opcode | Key Length |
+---------------+---------------+---------------+---------------+
4| Extras length | Data type | Status |
+---------------+---------------+---------------+---------------+
8| Total body length |
+---------------+---------------+---------------+---------------+
12| Opaque |
+---------------+---------------+---------------+---------------+
16| CAS |
| |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Header fields:
Magic Magic number.
Opcode Command code.
Key length Length in bytes of the text key that follows the
command extras.
Status Status of the response (non-zero on error).
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Extras length Length in bytes of the command extras.
Data type Reserved for future use (Sean is using this
soon).
Reserved Really reserved for future use (up for grabs).
Total body length Length in bytes of extra + key + value.
Opaque Will be copied back to you in the response.
CAS Data version check.
3. Defined Values
3.1. Magic Byte
0x80 Request packet for this protocol version
0x81 Response packet for this protocol version
Magic byte / version. For each version of the protocol, we'll use a
different request/response value pair. This is useful for protocol
analyzers to distinguish the nature of the packet from the direction
which it is moving. Note, it is common to run a memcached instance
on a host that also runs an application server. Such a host will
both send and receive memcache packets.
The version should hopefully correspond only to different meanings of
the command byte. In an ideal world, we will not change the header
format. As reserved bytes are given defined meaning, the protocol
version / magic byte values should be incremented.
Traffic analysis tools are encouraged to identify memcache packets
and provide detailed interpretation if the magic bytes are recognized
and otherwise to provide a generic breakdown of the packet. Note,
that the key and value positions can always be identified even if the
magic byte or command opcode are not recognized.
3.2. Response Status
Possible values of this two-byte field:
0x0000 No error
0x0001 Key not found
0x0002 Key exists
0x0003 Value too large
0x0004 Invalid arguments
0x0005 Item not stored
0x0006 Incr/Decr on non-numeric value.
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0x0081 Unknown command
0x0082 Out of memory
3.3. Command Opcodes
Possible values of the one-byte field:
0x00 Get
0x01 Set
0x02 Add
0x03 Replace
0x04 Delete
0x05 Increment
0x06 Decrement
0x07 Quit
0x08 Flush
0x09 GetQ
0x0A No-op
0x0B Version
0x0C GetK
0x0D GetKQ
0x0E Append
0x0F Prepend
0x10 Stat
0x11 SetQ
0x12 AddQ
0x13 ReplaceQ
0x14 DeleteQ
0x15 IncrementQ
0x16 DecrementQ
0x17 QuitQ
0x18 FlushQ
0x19 AppendQ
0x1A PrependQ
As a convention all of the commands ending with "Q" for Quiet. A
quiet version of a command will omit responses that are considered
uninteresting. Whether a given response is interesting is dependent
upon the command. See the descriptions of the set commands
(Section 4.2) and set commands (Section 4.3) for examples of commands
that include quiet variants.
3.4. Data Types
Possible values of the one-byte field:
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0x00 Raw bytes
4. Commands
4.1. Introduction
All communication is initiated by a request from the client, and the
server will respond to each request with zero or multiple packets for
each request. If the status code of a response packet is non-nil,
the body of the packet will contain a textual error message. If the
status code is nil, the command opcode will define the layout of the
body of the message.
4.1.1. Example
The following figure illustrates the packet layout for a packet with
an error message.
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Packet layout:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x01 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x09 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x4e ('N') | 0x6f ('o') | 0x74 ('t') | 0x20 (' ') |
+---------------+---------------+---------------+---------------+
28| 0x66 ('f') | 0x6f ('o') | 0x75 ('u') | 0x6e ('n') |
+---------------+---------------+---------------+---------------+
32| 0x64 ('d') |
+---------------+
Total 33 bytes (24 byte header, and 9 bytes value)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x00
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Status (6,7) : 0x0001
Total body (8-11) : 0x00000009
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : None
Value (24-32): The textual string "Not found"
4.2. Get, Get Quietly, Get Key, Get Key Quietly
Request:
MUST NOT have extras.
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MUST have key.
MUST NOT have value.
Response (if found):
MUST have extras.
MAY have key.
MAY have value.
o 4 byte flags
Extra data for the get commands:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Flags |
+---------------+---------------+---------------+---------------+
Total 4 bytes
The get command gets a single key. The getq command is both mum on
cache miss and quiet, holding its response until a non-quiet command
is issued. Getk and getkq differs from get and getq by adding the
key into the response packet.
You're not guaranteed a response to a getq/getkq cache hit until you
send a non-getq/getkq command later, which uncorks the server and
bundles up IOs to send to the client in one go.
Clients should implement multi-get (still important for reducing
network roundtrips!) as n pipelined requests, the first n-1 being
getq/getkq, the last being a regular get/getk. That way you're
guaranteed to get a response, and you know when the server's done.
You can also do the naive thing and send n pipelined get/getks, but
then you could potentially get back a lot of "NOT_FOUND" error code
packets. Alternatively, you can send 'n' getq/getkqs, followed by a
'noop' command.
4.2.1. Example
To request the data associated with the key "Hello" the following
fields must be specified in the packet.
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get request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x48 ('H') | 0x65 ('e') | 0x6c ('l') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
28| 0x6f ('o') |
+---------------+
Total 29 bytes (24 byte header, and 5 bytes key)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x00
Key length (2,3) : 0x0005
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000005
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key (24-29): The textual string: "Hello"
Value : None
If the item exist on the server the following packet is returned,
otherwise a packet with status code != 0 will be returned (see
Introduction (Section 4.1))
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get/getq response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x04 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x09 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x01 |
+---------------+---------------+---------------+---------------+
24| 0xde | 0xad | 0xbe | 0xef |
+---------------+---------------+---------------+---------------+
28| 0x57 ('W') | 0x6f ('o') | 0x72 ('r') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
32| 0x64 ('d') |
+---------------+
Total 33 bytes (24 byte header, 4 byte extras and 5 byte value)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x00
Key length (2,3) : 0x0000
Extra length (4) : 0x04
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000009
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000001
Extras :
Flags (24-27): 0xdeadbeef
Key : None
Value (28-32): The textual string "World"
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getk/getkq response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
4| 0x04 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x09 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x01 |
+---------------+---------------+---------------+---------------+
24| 0xde | 0xad | 0xbe | 0xef |
+---------------+---------------+---------------+---------------+
28| 0x48 ('H') | 0x65 ('e') | 0x6c ('l') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
32| 0x6f ('o') | 0x57 ('W') | 0x6f ('o') | 0x72 ('r') |
+---------------+---------------+---------------+---------------+
36| 0x6c ('l') | 0x64 ('d') |
+---------------+---------------+
Total 38 bytes (24 byte header, 4 byte extras, 5 byte key
and 5 byte value)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x00
Key length (2,3) : 0x0005
Extra length (4) : 0x04
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000009
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000001
Extras :
Flags (24-27): 0xdeadbeef
Key (28-32): The textual string: "Hello"
Value (33-37): The textual string: "World"
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4.3. Set, Add, Replace
MUST have extras.
MUST have key.
MUST have value.
o 4 byte flags
o 4 byte expiration time
Extra data for set/add/replace:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Flags |
+---------------+---------------+---------------+---------------+
4| Expiration |
+---------------+---------------+---------------+---------------+
Total 8 bytes
If the Data Version Check (CAS) is nonzero, the requested operation
MUST only succeed if the item exists and has a CAS value identical to
the provided value.
Add MUST fail if the item already exist.
Replace MUST fail if the item doesn't exist.
Set should store the data unconditionally if the item exists or not.
Quiet mutations only return responses on failure. Success is
considered the general case and is suppressed when in quiet mode, but
errors should not be allowed to go unnoticed.
4.3.1. Example
The following figure shows an add-command for
Key: "Hello"
Value: "World"
Flags: 0xdeadbeef
Expiry: in two hours
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Add request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x02 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
4| 0x08 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x12 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0xde | 0xad | 0xbe | 0xef |
+---------------+---------------+---------------+---------------+
28| 0x00 | 0x00 | 0x0e | 0x10 |
+---------------+---------------+---------------+---------------+
32| 0x48 ('H') | 0x65 ('e') | 0x6c ('l') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
36| 0x6f ('o') | 0x57 ('W') | 0x6f ('o') | 0x72 ('r') |
+---------------+---------------+---------------+---------------+
40| 0x6c ('l') | 0x64 ('d') |
+---------------+---------------+
Total 42 bytes (24 byte header, 8 byte extras, 5 byte key and
5 byte value)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x02
Key length (2,3) : 0x0005
Extra length (4) : 0x08
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000012
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras :
Flags (24-27): 0xdeadbeef
Expiry (28-31): 0x00000e10
Key (32-36): The textual string "Hello"
Value (37-41): The textual string "World"
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The response-packet contains no extra data, and the result of the
operation is signaled through the status code. If the command
succeeds, the CAS value for the item is returned in the CAS-field of
the packet.
Successful add response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x02 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x01 |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x02
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000000
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000001
Extras : None
Key : None
Value : None
4.4. Delete
MUST NOT have extras.
MUST have key.
MUST NOT have value.
Delete the item with the specific key.
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4.4.1. Example
The following figure shows a delete message for the item "Hello".
Delete request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x04 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x48 ('H') | 0x65 ('e') | 0x6c ('l') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
28| 0x6f ('o') |
+---------------+
Total 29 bytes (24 byte header, 5 byte value)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x04
Key length (2,3) : 0x0005
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000005
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : The textual string "Hello"
Value : None
The response-packet contains no extra data, and the result of the
operation is signaled through the status code.
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4.5. Increment, Decrement
MUST have extras.
MUST have key.
MUST NOT have value.
o 8 byte value to add / subtract
o 8 byte initial value (unsigned)
o 4 byte expiration time
Extra data for incr/decr:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Amount to add |
| |
+---------------+---------------+---------------+---------------+
8| Initial value |
| |
+---------------+---------------+---------------+---------------+
16| Expiration |
+---------------+---------------+---------------+---------------+
Total 20 bytes
These commands will either add or remove the specified amount to the
requested counter.
If the counter does not exist, one of two things may happen:
1. If the expiration value is all one-bits (0xffffffff), the
operation will fail with NOT_FOUND.
2. For all other expiration values, the operation will succeed by
seeding the value for this key with the provided initial value to
expire with the provided expiration time. The flags will be set
to zero.
incr/decr response body:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 64-bit unsigned response. |
| |
+---------------+---------------+---------------+---------------+
Total 8 bytes
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4.5.1. Example
The following figure shows an incr-command for
Key: "counter"
Delta: 0x01
Initial: 0x00
Expiry: in two hours
Increment request:
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Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x05 | 0x00 | 0x07 |
+---------------+---------------+---------------+---------------+
4| 0x14 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x1b |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
28| 0x00 | 0x00 | 0x00 | 0x01 |
+---------------+---------------+---------------+---------------+
32| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
36| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
40| 0x00 | 0x00 | 0x0e | 0x10 |
+---------------+---------------+---------------+---------------+
44| 0x63 ('c') | 0x6f ('o') | 0x75 ('u') | 0x6e ('n') |
+---------------+---------------+---------------+---------------+
48| 0x74 ('t') | 0x65 ('e') | 0x72 ('r') |
+---------------+---------------+---------------+
Total 51 bytes (24 byte header, 20 byte extras, 7 byte key)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x05
Key length (2,3) : 0x0007
Extra length (4) : 0x14
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x0000001b
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras :
delta (24-31): 0x0000000000000001
initial (32-39): 0x0000000000000000
exipration (40-43): 0x00000e10
Key : Textual string "counter"
Value : None
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If the key doesn't exist, the server will respond with the initial
value. If not the incremented value will be returned. Let's assume
that the key didn't exist, so the initial value is returned.
Increment response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x05 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x08 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
24| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
28| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
Total 32 bytes (24 byte header, 8 byte value)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x05
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000008
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000005
Extras : None
Key : None
Value : 0x0000000000000000
4.6. quit
MUST NOT have extras.
MUST NOT have key.
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MUST NOT have value.
Close the connection to the server.
4.6.1. Example
Quit request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x07 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x07
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000000
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : None
Value : None
The response-packet contains no extra data, and the result of the
operation is signaled through the status code. The server will then
close the connection.
4.7. Flush
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MAY have extras.
MUST NOT have key.
MUST NOT have value.
o 4 byte expiration time
Extra data for flush:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| Expiration |
+---------------+---------------+---------------+---------------+
Total 4 bytes
Flush the items in the cache now or some time in the future as
specified by the expiration field. See the documentation of the
textual protocol for the full description on how to specify the
expiration time.
4.7.1. Example
To flush the cache (delete all items) in two hours, the set the
following values in the request
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Flush request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x08 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x04 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x04 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x00 | 0x00 | 0x0e | 0x10 |
+---------------+---------------+---------------+---------------+
Total 28 bytes (24 byte header, 4 byte body)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x08
Key length (2,3) : 0x0000
Extra length (4) : 0x04
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000004
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras :
Expiry (24-27): 0x000e10
Key : None
Value : None
The response-packet contains no extra data, and the result of the
operation is signaled through the status code.
4.8. noop
MUST NOT have extras.
MUST NOT have key.
MUST NOT have value.
Used as a keep alive. Flushes outstanding getq/getkq's.
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4.8.1. Example
Noop request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x0a | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x0a
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000000
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : None
Value : None
The response-packet contains no extra data, and the result of the
operation is signaled through the status code.
4.9. version
MUST NOT have extras.
MUST NOT have key.
MUST NOT have value.
Request the server version.
The server responds with a packet containing the version string in
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the body with the following format: "x.y.z"
4.9.1. Example
Version request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x0b | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x0b
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000000
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
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Version response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x0b | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x31 ('1') | 0x2e ('.') | 0x33 ('3') | 0x2e ('.') |
+---------------+---------------+---------------+---------------+
28| 0x31 ('1') |
+---------------+
Total 29 bytes (24 byte header, 5 byte body)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x0b
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000005
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : None
Value : Textual string "1.3.1"
4.10. Append, Prepend
MUST NOT have extras.
MUST have key.
MUST have value.
These commands will either append or prepend the specified value to
the requested key.
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4.10.1. Example
The following example appends '!' to the 'Hello' key.
Append request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x0e | 0x00 | 0x05 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x06 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x48 ('H') | 0x65 ('e') | 0x6c ('l') | 0x6c ('l') |
+---------------+---------------+---------------+---------------+
28| 0x6f ('o') | 0x21 ('!') |
+---------------+---------------+
Total 30 bytes (24 byte header, 5 byte key, 1 byte value)
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x0e
Key length (2,3) : 0x0005
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000006
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key (24-28): The textual string "Hello"
Value (29) : "!"
The response-packet contains no extra data, and the result of the
operation is signaled through the status code.
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4.11. Stat
MUST NOT have extras.
MAY have key.
MUST NOT have value.
Request server statistics. Without a key specified the server will
respond with a "default" set of statistics information. Each piece
of statistical information is returned in its own packet (key
contains the name of the statistical item and the body contains the
value in ASCII format). The sequence of return packets is terminated
with a packet that contains no key and no value.
4.11.1. Example
The following example requests all statistics from the server
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Stat request:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x80 | 0x10 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
Total 24 bytes
Field (offset) (value)
Magic (0) : 0x80
Opcode (1) : 0x10
Key length (2,3) : 0x0000
Extra length (4) : 0x00
Data type (5) : 0x00
Reserved (6,7) : 0x0000
Total body (8-11) : 0x00000000
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Extras : None
Key : None
Value : None
The server will send each value in a separate packet with an "empty"
packet (no key / no value) to terminate the sequence. Each of the
response packets look like the following example:
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Stat response:
Byte/ 0 | 1 | 2 | 3 |
/ | | | |
|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
+---------------+---------------+---------------+---------------+
0| 0x81 | 0x10 | 0x00 | 0x03 |
+---------------+---------------+---------------+---------------+
4| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
8| 0x00 | 0x00 | 0x00 | 0x07 |
+---------------+---------------+---------------+---------------+
12| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
16| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
20| 0x00 | 0x00 | 0x00 | 0x00 |
+---------------+---------------+---------------+---------------+
24| 0x70 ('p') | 0x69 ('i') | 0x64 ('d') | 0x33 ('3') |
+---------------+---------------+---------------+---------------+
28| 0x30 ('0') | 0x37 ('7') | 0x38 ('8') |
+---------------+---------------+---------------+
Total 31 bytes (24 byte header, 3 byte key, 4 byte body)
Field (offset) (value)
Magic (0) : 0x81
Opcode (1) : 0x10
Key length (2,3) : 0x0003
Extra length (4) : 0x00
Data type (5) : 0x00
Status (6,7) : 0x0000
Total body (8-11) : 0x00000007
Opaque (12-15): 0x00000000
CAS (16-23): 0x0000000000000000
Exstras : None
Key : The textual string "pid"
Value : The textual string "3078"
5. Security Considerations
Memcache has no authentication or security layers whatsoever. It is
RECOMMENDED that memcache be deployed strictly on closed, protected,
back-end networks within a single data center, within a single
cluster of servers, or even on a single host, providing shared
caching for multiple applications. Memcache MUST NOT be made
available on a public network.
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6. Normative References
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[LJ] Danga Interactive, "LJ NEEDS MOAR SPEED", 10 1999.
Appendix A. Acknowledgments
Thanks to Brad Fitzpatrick, Anatoly Vorobey, Steven Grimm, and Dustin
Sallings, for their work on the memcached server.
Thanks to Sean Chittenden, Jonathan Steinert, Brian Aker, Evan
Martin, Nathan Neulinger, Eric Hodel, Michael Johnson, Paul Querna,
Jamie McCarthy, Philip Neustrom, Andrew O'Brien, Josh Rotenberg,
Robin H. Johnson, Tim Yardley, Paolo Borelli, Eli Bingham, Jean-
Francois Bustarret, Paul G, Paul Lindner, Alan Kasindorf, Chris
Goffinet, Tomash Brechko, and others for their work reporting bugs
and maintaining memcached client libraries and bindings in many
languages.
Authors' Addresses
Aaron Stone (editor)
Six Apart, Ltd.
548 4th Street
San Francisco, CA 94107
USA
Email: aaron@serendipity.palo-alto.ca.us
Trond Norbye (editor)
Sun Microsystems, INC
Haakon VII g. 7B
Trondheim NO-7485 Trondheim
Norway
Email: trond.norbye@sun.com
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