- Introduction
- Packet Structure
- Defined Values
- Commands
- Security Considerations
- Normative References
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.
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 inBinaryProtocolRevamped.
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
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 | vbucket id | +---------------+---------------+---------------+---------------+ 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 description
MagicMagic number identifying the package (See BinaryProtocolRevamped#Magic_Byte) OpcodeCommand code (See BinaryProtocolRevamped#Command_opcodes) Key lengthLength in bytes of the text key that follows the command extras StatusStatus of the response (non-zero on error) (See BinaryProtocolRevamped#Response_Status) Extras lengthLength in bytes of the command extras Data typeReserved for future use (See BinaryProtocolRevamped#Data_Type) vbucket idThe virtual bucket for this command Total body lengthLength in bytes of extra + key + value OpaqueWill be copied back to you in the response CASData version check
Defined Values
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.
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. |
| 0x0007 | The vbucket belongs to another server |
| 0x0008 | Authentication error |
| 0x0009 | Authentication continue |
| 0x0081 | Unknown command |
| 0x0082 | Out of memory |
| 0x0083 | Not supported |
| 0x0084 | Internal error |
| 0x0085 | Busy |
| 0x0086 | Temporary failure |
Command Opcodes
Possible values of the one-byte field. See BinaryProtocolRevamped#Commands for more information about a given command.
| 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 |
| 0x1b | Verbosity |
| 0x1c | Touch |
| 0x1d | GAT |
| 0x1e | GATQ |
| 0x20 | SASL list mechs |
| 0x21 | SASL Auth |
| 0x22 | SASL Step |
| 0x30 | RGet |
| 0x31 | RSet |
| 0x32 | RSetQ |
| 0x33 | RAppend |
| 0x34 | RAppendQ |
| 0x35 | RPrepend |
| 0x36 | RPrependQ |
| 0x37 | RDelete |
| 0x38 | RDeleteQ |
| 0x39 | RIncr |
| 0x3a | RIncrQ |
| 0x3b | RDecr |
| 0x3c | RDecrQ |
| 0x3d | Set VBucket |
| 0x3e | Get VBucket |
| 0x3f | Del VBucket |
| 0x40 | TAP Connect |
| 0x41 | TAP Mutation |
| 0x42 | TAP Delete |
| 0x43 | TAP Flush |
| 0x44 | TAP Opaque |
| 0x45 | TAP VBucket Set |
| 0x46 | TAP Checkpoint Start |
| 0x47 | TAP Checkpoint End |
Commands marked with is not currently fixed, but this is the current proposal for 1.6.
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.
Data Types
Possible values of the one-byte field:
| 0x00 | Raw bytes |
Commands
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.
Example
The following figure illustrates the packet layout for a packet with an error message.
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"
Get, Get Quietly, Get Key, Get Key Quietly
Request:
- MUST NOT have extras.
- MUST have key.
- MUST NOT have value.
Response (if found):
- MUST have extras.
- MAY have key.
- MAY have value.
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 will not send a response on a cache miss. Getk and getkq differs from get and getq by adding the key into the response packet.
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.
Example
To request the data associated with the key "Hello" the following fields must be specified in the 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| 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
VBucket (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))
The response packet for a getk and getkq request differs from get(q) in that the key is present:
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"
Set, Add, Replace
Request:
- MUST have extras.
- MUST have key.
- MUST have value.
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
Response:
- MUST have CAS
- MUST NOT have extras
- MUST NOT have key
- MUST NOT have value
Constraints:
- 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.
Example
The following figure shows an add-command for with key = "Hello", value = "World", flags = 0xdeadbeef and expiry: in two hours.
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 VBucket (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"
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:
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
Delete
Request:
- MUST NOT have extras.
- MUST have key.
- MUST NOT have value.
Response:
- MUST NOT have extras
- MUST NOT have key
- MUST NOT have value
Example
The following figure shows a delete message for the item "Hello".
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 VBucket (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 result of the operation is signaled through the status code.
Increment, Decrement
Request:
- MUST have extras.
- MUST have key.
- MUST NOT have value.
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 / subtract | | | +---------------+---------------+---------------+---------------+ 8| Initial value | | | +---------------+---------------+---------------+---------------+ 16| Expiration | +---------------+---------------+---------------+---------------+ Total 20 bytes
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST have value.
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
These commands will either add or remove the specified amount to the requested counter. If you want to set the value of the counter with add/set/replace, the objects data must be the ascii representation of the value and not the byte values of a 64 bit integer.
If the counter does not exist, one of two things may happen:
- 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 byseeding the value for this key with the provided initial value to expire with the provided expiration time. The flags will be set to zero.
Decrementing a counter will never result in a "negative value" (or cause the counter to "wrap"). instead the counter is set to 0. Incrementing the counter may cause the counter to wrap.
Example
The following figure shows an incr-command for key = "counter", delta = 0x01, initial = 0x00 which expires in two hours.
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 VBucket (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
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:
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
quit
Request:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Close the connection to the server.
Example
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 VBucket (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.
Flush
Request:
- MAY have extras.
- MUST NOT have key.
- MUST NOT have value.
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
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
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.
Example
To flush the cache (delete all items) in two hours, the set the following values in the 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 VBucket (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 result of the operation is signaled through the status code.
noop
Request:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Used as a keep alive.
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 VBucket (6,7) : 0x0000 Total body (8-11) : 0x00000000 Opaque (12-15): 0x00000000 CAS (16-23): 0x0000000000000000 Extras : None Key : None Value : None
The result of the operation is signaled through the status code.
version
Request:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST have value.
Request the server version.
The server responds with a packet containing the version string in the body with the following format: "x.y.z"
Example
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 VBucket (6,7) : 0x0000 Total body (8-11) : 0x00000000 Opaque (12-15): 0x00000000 CAS (16-23): 0x0000000000000000 Extras : None
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"
Append, Prepend
Request:
- MUST NOT have extras.
- MUST have key.
- MUST have value.
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
- MUST have CAS
These commands will either append or prepend the specified value to the requested key.
Example
The following example appends '!' to the 'Hello' key.
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 VBucket (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 result of the operation is signaled through the status code.
Stat
Request:
- MUST NOT have extras.
- MAY have key.
- MUST NOT have value.
Response:
- MUST NOT have extras.
- MAY have key.
- MAY 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.
Example
The following example requests all statistics from the server
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 VBucket (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:
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"
Verbosity
Request:
- MUST have extras.
- MUST NOT have key.
- MUST NOT have value.
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| Verbosity |
+---------------+---------------+---------------+---------------+
Total 4 bytes
Response:
- MUST NOT have extras.
- MUST NOT have key.
- MUST NOT have value.
Set the verbosity level of the server. This may cause your memcached server to generate more or less output.
Example
To set the verbosity level to two, set the following values in the request
@todo add me
The result of the operation is signaled through the status code.
Touch, GAT and GATQ
Request:
- MUST have extras.
- MUST have key.
- MUST NOT have value.
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| Expiration |
+---------------+---------------+---------------+---------------+
Total 4 bytes
Touch is used to set a new expiration time for an existing item. GAT (Get and touch) and GATQ will return the value for the object if it is present in the cache.
Example
@todo add me
Get/Set/Del VBucket
@todo add me
TAP Connect
@todo add me
TAP Mutation / Delete / Flush
@todo add me
TAP Opaque
@todo add me
TAP VBucket set
@todo add me
TAP Checkpoint start/stop
@todo add me
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.
Normative References
KEYWORDSBradner, 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.
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