git.m6w6.name Git - awesomized/libmemcached/blob - memcached/doc/protocol-binary-range.xml

   1 <?xml version="1.0" encoding="US-ASCII"?>
   2 <!DOCTYPE rfc SYSTEM "xml2rfc/rfc2629.dtd">
   3 <?xml-stylesheet type='text/xsl' href='xml2rfc/rfc2629.xslt'?>
   4 <?rfc toc="yes"?>
   5 <?rfc strict="yes"?>
   6 <?rfc symrefs="yes"?>
   7 <?rfc sortrefs="yes" ?>
   8 <?rfc compact="yes" ?>
   9 <?rfc subcompact="yes" ?>
  10 <rfc category="info" docName="draft-stone-memcache-udp-01" ipr="none">
  11
  12   <front>
  13
  14     <title abbrev="Memcache Over UDP"> Memcache Binary Protocol: Extensions for UDP </title>
  15
  16     <author fullname="Aaron Stone" surname="Aaron Stone" role="editor">
  17       <organization>Six Apart, Ltd.</organization>
  18       <address>
  19         <postal>
  20           <street>548 4th Street</street>
  21           <city>San Francisco</city>
  22           <region>CA</region>
  23           <code>94107</code>
  24           <country>USA</country>
  25         </postal>
  26         <email>aaron@serendipity.palo-alto.ca.us</email>
  27       </address>
  28     </author>
  29
  30     <date day="14" month="December" year="2007" />
  31
  32     <area>Applications</area>
  33
  34     <keyword>memcache memcached cache udp</keyword>
  35
  36     <abstract>
  37       <t>
  38       This memo explains extensions to the memcache binary protocol for use in a UDP environment.
  39       </t>
  40
  41       <t>
  42       Memcache is a high performance key-value cache. It is intentionally a
  43       dumb cache, optimized for speed only. Applications using memcache do
  44       not rely on it for data -- a persistent database with guaranteed reliability
  45       is strongly recommended -- but applications can run much faster when
  46       cached data is available in memcache.
  47       </t>
  48     </abstract>
  49   </front>
  50
  51   <middle>
  52     <section anchor="introduction" title="Introduction">
  53       <t>
  54       Memcache is a high performance key-value cache. It is intentionally a
  55       dumb cache, optimized for speed only. Applications using memcache do
  56       not rely on it for data -- a persistent database with guaranteed reliability
  57       is strongly recommended -- but applications can run much faster when
  58       cached data is available in memcache.
  59       </t>
  60       <t>
  61       Sites may find that, due to their network architecture or application usage patterns,
  62       the stateless <xref target="UDP"/> protocol better suits their needs. This document
  63       provides extensions and descriptions of use of the <xref target="MEMCACHE">memcache protocol</xref>
  64       in a UDP environment.
  65       </t>
  66       <t>
  67       It is a goal of this document to provide sufficient information in each UDP packet
  68       as to avoid any requirement for statefulness on the part of the server nor significant
  69       caching of outstanding packets on the part of the client.
  70       </t>
  71       <section anchor="conventions" title="Conventions Used In This Document">
  72         <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  73         "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  74         document are to be interpreted as described in <xref target="KEYWORDS"/>.
  75         </t>
  76       </section>
  77     </section>
  78
  79     <section anchor="values" title="Defined Values">
  80       <section anchor="value-magic" title="Magic Byte">
  81         <t>
  82         The magic bytes remains the same as in <xref target="MEMCACHE"/>.
  83         </t>
  84       </section>
  85
  86       <section anchor="value-status" title="Response Status">
  87         <t>
  88         Additional status values:
  89         <list hangIndent="8" style="hanging">
  90           <t hangText="0x0004">Value is larger than a single response packet</t>
  91         </list>
  92         </t>
  93       </section>
  94
  95       <section anchor="value-opcodes" title="Command Opcodes">
  96         <t>
  97         Additional opcode values:
  98         <list hangIndent="8" style="hanging">
  99           <t hangText="0x0C">Get Range</t>
 100           <t hangText="0x0D">Set Range</t>
 101         </list>
 102         </t>
 103       </section>
 104
 105       <section anchor="value-types" title="Data Types">
 106         <t>
 107         There are no new data types in this extension.
 108         </t>
 109       </section>
 110     </section>
 111
 112     <section anchor="commands" title="Commands">
 113
 114       <section anchor="command-get" title="Get Response">
 115         <t>
 116         This section extends the behavior of the Get and GetQ commands as described in
 117         <xref target="MEMCACHE" x:sec="command-get"/>.
 118         </t>
 119
 120         <t>
 121         When a Get or GetQ request is made via UDP, and the value of the key for which
 122         the request was made is larger than can be placed into a single UDP packet (noting
 123         that the protocol header must also be counted), a Get Range response packet
 124         MUST be sent instead of the Get response packet. In this instance:
 125         <list style="numbers">
 126           <t>The Status field of the response header MUST be 0x0004.</t>
 127           <t>The Offset field of the GetR response extras MUST be 0.</t>
 128           <t>The Length field of the GetR response extras, and the data contained in
 129              the Value field of the packet, SHOULD be the maximum
 130              allowed length of a UDP packet, less the space required by the header
 131              and extras; however it MAY be any amount below this maximum.</t>
 132           <t>The Total value length field of the response extras MUST be the
 133              actual length of the complete value.</t>
 134         </list>
 135         </t>
 136
 137         <t>
 138         The client, upon receipt of a Get Range response bearing Status 0x004
 139         and a Message ID corresponding to its Get request, shall then know that
 140         it has received only the first portion of the value. The client MAY choose
 141         to request the remaining portion of the value by sending one or more Get Range requests.
 142         </t>
 143       </section>
 144
 145       <section anchor="command-getr-request" title="Get Range Request">
 146         <t>
 147           The Get Range request is primarily intended for use over a UDP transport
 148           to request byte ranges of the value for a key. In the event that the Data version
 149           check fails to match that of the key, an error MUST be returned.
 150         </t>
 151         <t>
 152       <figure>
 153         <preamble>Extra data for get range request:</preamble>
 154           <artwork>
 155 Byte/     0       |       1       |       2       |       3       |
 156    /              |               |               |               |
 157   |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|
 158   +---------------+---------------+---------------+---------------+
 159  0| Flags                                                         |
 160   +---------------+---------------+---------------+---------------+
 161  4| Data version check                                            |
 162   |                                                               |
 163   +---------------+---------------+---------------+---------------+
 164 12| Offset                                                        |
 165   +---------------+---------------+---------------+---------------+
 166 16| Length                                                        |
 167   +---------------+---------------+---------------+---------------+
 168 Total 20 bytes
 169       </artwork></figure>
 170         </t>
 171       </section>
 172
 173       <section anchor="command-getr-response" title="Get Range Response">
 174         <t>
 175           The Get Range request is primarily intended for use over a UDP transport
 176           to indicate the location of the bytes of the value for a key contained in
 177           a given packet. A client receives enough information in each Get Range
 178           extras to construct an appropriately sized buffer in its own memory and
 179           blindly insert the contents of the packet at the given byte offset.
 180         </t>
 181         <t>
 182       <figure>
 183         <preamble>Extra data for get range response:</preamble>
 184           <artwork>
 185 Byte/     0       |       1       |       2       |       3       |
 186    /              |               |               |               |
 187   |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|
 188   +---------------+---------------+---------------+---------------+
 189  0| Flags                                                         |
 190   +---------------+---------------+---------------+---------------+
 191  4| Data version check                                            |
 192   |                                                               |
 193   +---------------+---------------+---------------+---------------+
 194 12| Offset                                                        |
 195   +---------------+---------------+---------------+---------------+
 196 16| Length                                                        |
 197   +---------------+---------------+---------------+---------------+
 198 20| Total value length                                            |
 199   +---------------+---------------+---------------+---------------+
 200 Total 24 bytes
 201       </artwork></figure>
 202         </t>
 203       </section>
 204
 205     </section>
 206
 207     <section anchor="security" title="Security Considerations">
 208       <t>
 209       This document does not introduce any new security considerations
 210       beyond those discussed in <xref target="MEMCACHE" x:sec="security"/>.
 211       </t>
 212     </section>
 213
 214   </middle>
 215
 216   <back>
 217     <references title="Normative References">
 218       <dwdrfc-ref anchor='UDP' src='http://xml.resource.org/public/rfc/bibxml/reference.RFC.0768.xml'/>
 219       <dwdrfc-ref anchor='KEYWORDS' src='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'/>
 220       <!-- FIXME: Get a draft reference for the base document. -->
 221       <dwdrfc-ref anchor='MEMCACHE' src='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'/>
 222     </references>
 223   </back>
 224
 225 </rfc>
 226