Network Working Group Aaron Stone, Ed.
Internet-Draft Six Apart, Ltd.
Intended status: Informational December 14, 2007
Expires: June 16, 2008
Memcache Binary Protocol: Extensions for UDP
draft-stone-memcache-udp-01
Abstract
This memo explains extensions to the memcache binary protocol for use
in a UDP environment.
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.
Status of This Memo
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This Internet-Draft will expire on June 16, 2008.
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Copyright (c) 2007 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used In This Document . . . . . . . . . . . . 2
2. Defined Values . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Magic Byte . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Response Status . . . . . . . . . . . . . . . . . . . . . 3
2.3. Command Opcodes . . . . . . . . . . . . . . . . . . . . . 3
2.4. Data Types . . . . . . . . . . . . . . . . . . . . . . . 3
3. Commands . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Get Response . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Get Range Request . . . . . . . . . . . . . . . . . . . . 4
3.3. Get Range Response . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
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.
Sites may find that, due to their network architecture or application
usage patterns, the stateless [UDP] protocol better suits their
needs. This document provides extensions and descriptions of use of
the memcache protocol [MEMCACHE] in a UDP environment.
It is a goal of this document to provide sufficient information in
each UDP packet as to avoid any requirement for statefulness on the
part of the server nor significant caching of outstanding packets on
the part of the client.
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].
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2. Defined Values
2.1. Magic Byte
The magic bytes remains the same as in [MEMCACHE].
2.2. Response Status
Additional status values:
0x0004 Value is larger than a single response packet
2.3. Command Opcodes
Additional opcode values:
0x0C Get Range
0x0D Set Range
2.4. Data Types
There are no new data types in this extension.
3. Commands
3.1. Get Response
This section extends the behavior of the Get and GetQ commands as
described in [MEMCACHE].
When a Get or GetQ request is made via UDP, and the value of the key
for which the request was made is larger than can be placed into a
single UDP packet (noting that the protocol header must also be
counted), a Get Range response packet MUST be sent instead of the Get
response packet. In this instance:
1. The Status field of the response header MUST be 0x0004.
2. The Offset field of the GetR response extras MUST be 0.
3. The Length field of the GetR response extras, and the data
contained in the Value field of the packet, SHOULD be the maximum
allowed length of a UDP packet, less the space required by the
header and extras; however it MAY be any amount below this
maximum.
4. The Total value length field of the response extras MUST be the
actual length of the complete value.
The client, upon receipt of a Get Range response bearing Status 0x004
and a Message ID corresponding to its Get request, shall then know
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that it has received only the first portion of the value. The client
MAY choose to request the remaining portion of the value by sending
one or more Get Range requests.
3.2. Get Range Request
The Get Range request is primarily intended for use over a UDP
transport to request byte ranges of the value for a key. In the
event that the Data version check fails to match that of the key, an
error MUST be returned.
Extra data for get range 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| Flags |
+---------------+---------------+---------------+---------------+
4| Data version check |
| |
+---------------+---------------+---------------+---------------+
12| Offset |
+---------------+---------------+---------------+---------------+
16| Length |
+---------------+---------------+---------------+---------------+
Total 20 bytes
3.3. Get Range Response
The Get Range request is primarily intended for use over a UDP
transport to indicate the location of the bytes of the value for a
key contained in a given packet. A client receives enough
information in each Get Range extras to construct an appropriately
sized buffer in its own memory and blindly insert the contents of the
packet at the given byte offset.
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Extra data for get range 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| Flags |
+---------------+---------------+---------------+---------------+
4| Data version check |
| |
+---------------+---------------+---------------+---------------+
12| Offset |
+---------------+---------------+---------------+---------------+
16| Length |
+---------------+---------------+---------------+---------------+
20| Total value length |
+---------------+---------------+---------------+---------------+
Total 24 bytes
4. Security Considerations
This document does not introduce any new security considerations
beyond those discussed in [MEMCACHE].
5. Normative References
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[MEMCACHE]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
Author's Address
Aaron Stone (editor)
Six Apart, Ltd.
548 4th Street
San Francisco, CA 94107
USA
Email: aaron@serendipity.palo-alto.ca.us
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