root/branches/binary/server/doc/protocol-binary-range.txt @ 776

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

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
   with any rights other than to publish as an Internet-Draft.

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   This Internet-Draft will expire on June 16, 2008.

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.








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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Conventions Used In This Document . . . . . . . . . . . . . 3
   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  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Get Response  . . . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Get Range Request . . . . . . . . . . . . . . . . . . . . . 4
     3.3.  Get Range Response  . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6



































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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
   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].


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.






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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
   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.

















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   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.

   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







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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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