Commit aed57a31 authored by antirez's avatar antirez
Browse files

html doc rebuild

parent 73287b2b
This diff is collapsed.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>Features: Contents</b><br>&nbsp;&nbsp;<a href="#Features (DRAFT)">Features (DRAFT)</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Speed">Speed</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Persistence">Persistence</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Support for Data Structures">Support for Data Structures</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Atomic Operations">Atomic Operations</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Variety of Supported Languages">Variety of Supported Languages</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Master/Slave Replication">Master/Slave Replication</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Sharding">Sharding</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Hot Backups">Hot Backups</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Simple to Install, Setup and Manage">Simple to Install, Setup and Manage</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Portable">Portable</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Liberal Licensing">Liberal Licensing</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#What's next?">What's next?</a>
</div>
<h1 class="wikiname">Features</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="SideBar.html">SideBar</a>
<h1><a name="Features (DRAFT)">Features (DRAFT)</a></h1>Checking Redis for the first time? Here your will find the most important features, and pointers to a lot more information.<h2><a name="Speed">Speed</a></h2>Redis is written in ANSI C, and loads the whole dataset in memory, so it is wicked <i><b>fast</b>!</i> Up to 110,000 <a href="SETs.html">SETs</a>/second, 81,000 GETs/second can be achieved in an entry level Linux box. Read more about Redis <a href="Speed.html">Speed</a>.<br/><br/>Also Redis supports <a href="Pipelining.html">Pipelining</a> of commands and <a href="MultiBulkCommands.html">getting and setting m&Atilde;&ordm;ltiple values in a single command</a> to speed up communication with the client libraries.<h2><a name="Persistence">Persistence</a></h2>While all the data lives in memory, changes are <i>asynchronously</i> saved on disk using flexible policies based on elapsed time and/or number of updates since last save. <br/><br/>If you can't afford losing some data, starting on version 1.1 (currently in beta but you can download it from the Git repository) Redis supports an append-only file persistence mode. Check more on <a href="Persistence.html">Persistence</a>, or read the <a href="AppendOnlyFileHowto.html">AppendOnlyFileHowto</a> for more information.<h2><a name="Support for Data Structures">Support for Data Structures</a></h2>Values in Redis can be <a href="Strings.html">Strings</a> as in a conventional key-value store, but also <a href="Lists.html">Lists</a>, <a href="Sets.html">Sets</a>, and <a href="SortedSets.html">SortedSets</a> (to be support in <a href="RoadMap.html">version 1.1</a>). This data types allow pushing/poping elements, or adding/removing them, also perform server side union, intersection, difference between sets, and so forth depending on the types. Redis supports different kind of sorting abilities for <a href="Sets.html">Sets</a> and <a href="Lists.html">Lists</a>.<br/><br/>You can think in Redis as a <b>Data Structures Server</b>, that allows you to model non trivial problems. Read <a href="DataTypes.html">Data Types</a> to learn more about the way Redis handle <a href="Strings.html">Strings</a>, and the <a href="Commands.html">Commands</a> supported by <a href="Lists.html">Lists</a>, <a href="Sets.html">Sets</a> and <a href="SortedSets.html">SortedSets</a><h2><a name="Atomic Operations">Atomic Operations</a></h2>Redis operations working on the different Data Types are <b>atomic</b>, so setting or increasing a key, adding and removing elements from a set, increasing a counter will all be accomplished safely.<h2><a name="Variety of Supported Languages">Variety of Supported Languages</a></h2>Ruby, Python, Twisted Python, PHP, Erlang, Tcl, Perl, Lua, Java, Scala, Clojure, choose your poison. Check the list of <a href="SupportedLanguages.html">Supported Languages</a> for all the details.<br/><br/>If your favorite language is not supported yet, you can write your own client library, as the <a href="ProtocolSpecification.html">Protocol</a> is pretty simple.<h2><a name="Master/Slave Replication">Master/Slave Replication</a></h2>Redis supports a very simple and fast Master/Slave replication. Is so simple it takes only one line in the <a href="Configuration.html">configuration file</a> to set it up, and 21 seconds for a Slave to complete the initial sync of 10 MM key set in a Amazon EC2 instance.<br/><br/>Read more about Master/Slave <a href="Replication.html">Replication</a>. <h2><a name="Sharding">Sharding</a></h2>Distributing the dataset across multiple Redis instances is easy in Redis, as in any other key-value store. And this depends basically on the <a href="Supported.html">Languages</a> client libraries being able to do so. <br/><br/>Read more about <a href="Sharding.html">Sharding</a> if you want to know more abour distributing data and workload in Redis.<h2><a name="Hot Backups">Hot Backups</a></h2>TODO<h2><a name="Simple to Install, Setup and Manage">Simple to Install, Setup and Manage</a></h2>Installing Redis requires little more than downloading it, uncompressing it and running make. Management is near zero, so you can start using Redis in a matter of minutes.<br/><br/>Go on and read about Redis <a href="Installation.html">installation</a>, its <a href="Setup.html">Setup</a> and <a href="Management.html">Management</a>.<h2><a name="Portable">Portable</a></h2>Redis is written in ANSI C and works in most POSIX systems like Linux, BSD, Mac OS X, Solaris, and so on. Redis is reported to compile and work under WIN32 if compiled with Cygwin, but there is no official support for Windows currently.<h2><a name="Liberal Licensing">Liberal Licensing</a></h2>Redis is free software released under the very liberal BSD license.<h2><a name="What's next?">What's next?</a></h2>Want to get started with Redis? Try the <a href="QuickStart.html">Quick Start</a> you will be up and running in just a matter of minutes. <br/><br/>Check the <a href="CodeSamples.html">Code Samples</a> and find how you can use Redis with your favorite programming language.<br/><br/><a href="Comparisons.html">Compare</a> Redis with other key-value stores, like Tokyo Cabinet or Memcached.
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>FlushallCommand: Contents</b><br>&nbsp;&nbsp;<a href="#FLUSHALL">FLUSHALL</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">FlushallCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="GenericCommandsSidebar.html">GenericCommandsSidebar</a><h1><a name="FLUSHALL">FLUSHALL</a></h1>
<blockquote>Delete all the keys of all the existing databases, not just the currently selected one. This command never fails.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>FlushdbCommand: Contents</b><br>&nbsp;&nbsp;<a href="#FLUSHDB">FLUSHDB</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">FlushdbCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="GenericCommandsSidebar.html">GenericCommandsSidebar</a><h1><a name="FLUSHDB">FLUSHDB</a></h1>
<blockquote>Delete all the keys of the currently selected DB. This command never fails.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>FromSqlToDataStructures: Contents</b><br>&nbsp;&nbsp;<a href="#Introduction (IDEA MORE THAN A DRAFT)">Introduction (IDEA MORE THAN A DRAFT)</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Data Structures">Data Structures</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Dude where is my SELECT statement?">Dude where is my SELECT statement?</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#LISTs">LISTs</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#SETs">SETs</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#SORT to the rescue">SORT to the rescue</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#SORT BY">SORT BY</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#HASHEs">HASHEs</a>
</div>
<h1 class="wikiname">FromSqlToDataStructures</h1>
<div class="summary">
</div>
<div class="narrow">
<h1><a name="Introduction (IDEA MORE THAN A DRAFT)">Introduction (IDEA MORE THAN A DRAFT)</a></h1><b>&Acirc;&iquest;Coming from SQLand?</b> <i>&Acirc;&iquest;Who doesn't?</i> Redis is simple, <i>primitive</i> when comapred to the world you are used to in the world of Relational Database Managers (RDBMS) and Structure Query Language (SQL), here you will find insight to build bridges between both worlds to model real life problems.<h2><a name="Data Structures">Data Structures</a></h2>When I was young, happy and single ;) I studied <b>Data Structures</b> at the university, actually I learnt Data Structures and Algorithms <i>before</i> learning anything about Databases, and particularly RDBMS and SQL. This is natural because you need to know about Data Structures and Algorithms to understand a Database.<br/><br/>Redis can be seen as a <b>Data Structures Server</b>, a very simple interface to a extremly fast and efficient <h2><a name="Dude where is my SELECT statement?">Dude where is my SELECT statement?</a></h2><h2><a name="LISTs">LISTs</a></h2>In SQL there is no such thing as a &quot;natural&quot; order, a SELECT statement without a ORDER BY clause will return data in a undefined order. In Redis <a href="LISTs.html">LISTs</a> address the problem of natural ordering, ...<h2><a name="SETs">SETs</a></h2>So you have a bunch of unordered data, <h2><a name="SORT to the rescue">SORT to the rescue</a></h2>But sometimes we <i>need</i> to actually sort a LIST in a order different from its natural or take a SET and have it ordered, there is where the <i>fast</i> SORT commands comes handy... <h3><a name="SORT BY">SORT BY</a></h3>Just SORTing keys would be kind of boring, sometimes useless right? Well, you can SORT...<h2><a name="HASHEs">HASHEs</a></h2>Umm, sorry you will have to wait for a <a href="RoadMap.html">upcoming version of Redis</a> to have Hashes, but here are Idioms you should house to manage Dictionary like data...
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>GenericCommandsSidebar: Contents</b>
</div>
<h1 class="wikiname">GenericCommandsSidebar</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;== Generic Commands ==<br/><br/><ul><li> <a href="ExistsCommand.html">EXISTS</a></li><li> <a href="DelCommand.html">DEL</a></li><li> <a href="TypeCommand.html">TYPE</a></li><li> <a href="KeysCommand.html">KEYS</a></li><li> <a href="RandomkeyCommand.html">RANDOMKEY</a></li><li> <a href="RenameCommand.html">RENAME</a></li><li> <a href="RenamenxCommand.html">RENAMENX</a></li><li> <a href="DbsizeCommand.html">DBSIZE</a></li><li> <a href="ExpireCommand.html">EXPIRE</a></li><li> <a href="TtlCommand.html">TTL</a></li><li> <a href="SelectCommand.html">SELECT</a></li><li> <a href="MoveCommand.html">MOVE</a></li><li> <a href="FlushdbCommand.html">FLUSHDB</a></li><li> <a href="FlushallCommand.html">FLUSHALL</a></li></ul>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>GetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#GET _key_">GET _key_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">GetCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="StringCommandsSidebar.html">StringCommandsSidebar</a><h1><a name="GET _key_">GET _key_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Get the value of the specified key. If the keydoes not exist the special value 'nil' is returned.If the value stored at <i>key</i> is not a string an erroris returned because GET can only handle string values.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>GetsetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#GETSET _key_ _value_">GETSET _key_ _value_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Design patterns">Design patterns</a>
</div>
<h1 class="wikiname">GetsetCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="StringCommandsSidebar.html">StringCommandsSidebar</a><h1><a name="GETSET _key_ _value_">GETSET _key_ _value_</a></h1>
<i>Time complexity: O(1)</i><blockquote>GETSET is an atomic <i>set this value and return the old value</i> command.Set <i>key</i> to the string <i>value</i> and return the old value stored at <i>key</i>.The string can't be longer than 1073741824 bytes (1 GB).</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a><h2><a name="Design patterns">Design patterns</a></h2><blockquote>GETSET can be used together with INCR for counting with atomic reset whena given condition arises. For example a process may call INCR against thekey <i>mycounter</i> every time some event occurred, but from time totime we need to get the value of the counter and reset it to zero atomicallyusing <code name="code" class="python">GETSET mycounter 0</code>.</blockquote>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HackingStrings: Contents</b><br>&nbsp;&nbsp;<a href="#Hacking Strings">Hacking Strings</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Creating Redis Strings">Creating Redis Strings</a>
</div>
<h1 class="wikiname">HackingStrings</h1>
<div class="summary">
</div>
<div class="narrow">
<h1><a name="Hacking Strings">Hacking Strings</a></h1>The implementation of Redis strings is contained in <b></b>sds.c<b></b> ( sds stands for Simple Dynamic Strings ).<br/><br/>The C structure <i>sdshdr</i> declared in <b>sds.h</b> represents a Redis string:<br/><br/><pre class="codeblock python" name="code">
struct sdshdr {
long len;
long free;
char buf[];
};
</pre>The <i>buf</i> character array stores the actual string.<br/><br/>The <i>len</i> field stores the length of <i>buf</i>. This makes obtaining the length
of a Redis string an O(1) operation.<br/><br/>The <i>free</i> field stores the number of additional bytes available for use.<br/><br/>Together the <i>len</i> and <i>free</i> field can be thought of as holding the metadata of the
<i>buf</i> character array.<h2><a name="Creating Redis Strings">Creating Redis Strings</a></h2>A new data type named <code name="code" class="python">sds</code> is defined in <b>sds.h</b> to be a synonymn for a character pointer:<br/><br/><pre class="codeblock python python" name="code">
typedef char *sds;
</pre><code name="code" class="python">sdsnewlen</code> function defined in <b>sds.c</b> creates a new Redis String: <br/><br/><pre class="codeblock python python python" name="code">
sds sdsnewlen(const void *init, size_t initlen) {
struct sdshdr *sh;
sh = zmalloc(sizeof(struct sdshdr)+initlen+1);
#ifdef SDS_ABORT_ON_OOM
if (sh == NULL) sdsOomAbort();
#else
if (sh == NULL) return NULL;
#endif
sh-&gt;len = initlen;
sh-&gt;free = 0;
if (initlen) {
if (init) memcpy(sh-&gt;buf, init, initlen);
else memset(sh-&gt;buf,0,initlen);
}
sh-&gt;buf[initlen] = '\0';
return (char*)sh-&gt;buf;
}
</pre>Remember a Redis string is a variable of type <code name="code" class="python">struct sdshdr</code>. But <code name="code" class="python">sdsnewlen</code> returns a character pointer!!<br/><br/>That's a trick and needs some explanation.<br/><br/>Suppose I create a Redis string using <code name="code" class="python">sdsnewlen</code> like below:<br/><br/><pre class="codeblock python python python python" name="code">
sdsnewlen(&quot;redis&quot;, 5);
</pre>This creates a new variable of type <code name="code" class="python">struct sdshdr</code> allocating memory for <i>len</i> and <i>free</i>
fields as well as for the <i>buf</i> character array.<br/><br/><pre class="codeblock python python python python python" name="code">
sh = zmalloc(sizeof(struct sdshdr)+initlen+1); // initlen is length of init argument.
</pre>After <code name="code" class="python">sdsnewlen</code> succesfully creates a Redis string the result is something like:<br/><br/><pre class="codeblock python python python python python python" name="code">
-----------
|5|0|redis|
-----------
^ ^
sh sh-&gt;buf
</pre><code name="code" class="python">sdsnewlen</code> returns sh-&gt;buf to the caller.<br/><br/>What do you do if you need to free the Redis string pointed by <code name="code" class="python">sh</code>?<br/><br/>You want the pointer <code name="code" class="python">sh</code> but you only have the pointer <code name="code" class="python">sh-&gt;buf</code>.<br/><br/>Can you get the pointer <code name="code" class="python">sh</code> from <code name="code" class="python">sh-&gt;buf</code>?<br/><br/>Yes. Pointer arithmetic. Notice from the above ASCII art that if you subtract
the size of two longs from <code name="code" class="python">sh-&gt;buf</code> you get the pointer <code name="code" class="python">sh</code>. <br/><br/>The sizeof two longs happens to be the size of <code name="code" class="python">struct sdshdr</code>.<br/><br/>Look at <code name="code" class="python">sdslen</code> function and see this trick at work:<br/><br/><pre class="codeblock python python python python python python python" name="code">
size_t sdslen(const sds s) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
return sh-&gt;len;
}
</pre>Knowing this trick you could easily go through the rest of the functions in <b>sds.c</b>.<br/><br/>The Redis string implementation is hidden behind an interface that accepts only character pointers. The users of Redis strings need not care about how its implemented and treat Redis strings as a character pointer.
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HashCommandsSidebar: Contents</b>
</div>
<h1 class="wikiname">HashCommandsSidebar</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;== Hash Commands ==<br/><br/><ul><li> <a href="HsetCommand.html">HSET</a></li><li> <a href="HgetCommand.html">HGET</a></li><li> <a href="HsetnxCommand.html">HSETNX</a></li><li> <a href="HmsetCommand.html">HMSET</a></li><li> <a href="HincrbyCommand.html">HINCRBY</a></li><li> <a href="HexistsCommand.html">HEXISTS</a></li><li> <a href="HdelCommand.html">HDEL</a></li><li> <a href="HlenCommand.html">HLEN</a></li><li> <a href="HgetallCommand.html">HKEYS</a></li><li> <a href="HgetallCommand.html">HVALS</a></li><li> <a href="HgetallCommand.html">HGETALL</a></li></ul>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>Hashes: Contents</b><br>&nbsp;&nbsp;<a href="#Redis Hash Type">Redis Hash Type</a><br>&nbsp;&nbsp;<a href="#Implementation details">Implementation details</a>
</div>
<h1 class="wikiname">Hashes</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="Redis Hash Type">Redis Hash Type</a></h1>Redis Hashes are unordered maps of <a href="String.html">Redis Strings</a> between fields and values. It is possible to add, remove, test for existence of fields in O(1) amortized time. It is also possible to enumerate all the keys, values, or both, in O(N) (where N is the number of fields inside the hash).<br/><br/>Redis Hashes are interesting because they are very well suited to represent objects. For instance web applications users can be represented by a Redis Hash containing fields such username, encrpypted_password, lastlogin, and so forth.<br/><br/>Another very important property of Redis Hashes is that they use very little memory for hashes composed of a small number of fields (configurable, check redis.conf for details), compared to storing every field as a top level Redis key. This is obtained using a different specialized representation for small hashes. See the implementation details paragraph below for more information.<br/><br/>Commands operating on hashes try to make a good use of the return value in order to signal the application about previous existence of fields. For instance the <a href="HsetCommand.html">HSET</a> command will return 1 if the field set was not already present in the hash, otherwise will return 0 (and the user knows this was just an update operation).<br/><br/>The max number of fields in a set is 232-1 (4294967295, more than 4 billion of members per hash).<h1><a name="Implementation details">Implementation details</a></h1>The obvious internal representation of hashes is indeed an hash table, as the name of the data structure itself suggests. Still the drawback of this representation is that there is a lot of space overhead for hash table metadata.<br/><br/>Because one of the most interesting uses of Hashes is object encoding, and objects are often composed of a few fields each, Redis uses a different internal representation for small hashes (for Redis to consider a hash small, this must be composed a limited number of fields, and each field and value can't exceed a given number of bytes. All this is user-configurable).<br/><br/>Small hashes are thus encoded using a data structure called zipmap (is not something you can find in a CS book, the name is a Redis invention), that is a very memory efficient data structure to represent string to string maps, at the cost of being O(N) instead of O(1) for most operations. Since the constant times of this data structure are very small, and the zipmaps are converted into real hash tables once they are big enough, the amortized time of Redis hashes is still O(1), and in the practice small zipmaps are not slower than small hash tables because they are designed for good cache locality and fast access.<br/><br/>The result is that small hashes are both memory efficient and fast, while bigger hashes are fast but not as memory efficient than small hashes.
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HdelCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HDEL _key_ _field_ (Redis &gt;">HDEL _key_ _field_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HdelCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HDEL _key_ _field_ (Redis &gt;">HDEL _key_ _field_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Remove the specified <i>field</i> from an hash stored at <i>key</i>.</blockquote>
<blockquote>If the <i>field</i> was present in the hash it is returned and 1 is returned, otherwise 0 is returned and no operation is performed.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HexistsCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HEXISTS _key_ _field_ (Redis &gt;">HEXISTS _key_ _field_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HexistsCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HEXISTS _key_ _field_ (Redis &gt;">HEXISTS _key_ _field_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Return 1 if the hash stored at <i>key</i> contains the specified <i>field</i>.</blockquote>
<blockquote>Return 0 if the <i>key</i> is not found or the <i>field</i> is not present.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HgetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HGET _key_ _field_ (Redis &gt;">HGET _key_ _field_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HgetCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HGET _key_ _field_ (Redis &gt;">HGET _key_ _field_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>If <i>key</i> holds a hash, retrieve the value associated to the specified <i>field</i>.</blockquote>
<blockquote>If the <i>field</i> is not found or the <i>key</i> does not exist, a special 'nil' value is returned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HgetallCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HKEYS _key_ (Redis &gt;">HKEYS _key_ (Redis &gt;</a><br>&nbsp;&nbsp;<a href="#HVALS _key_ (Redis &gt;">HVALS _key_ (Redis &gt;</a><br>&nbsp;&nbsp;<a href="#HGETALL _key_ (Redis &gt;">HGETALL _key_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HgetallCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HKEYS _key_ (Redis &gt;">HKEYS _key_ (Redis &gt;</a></h1> 1.3.10)=
<h1><a name="HVALS _key_ (Redis &gt;">HVALS _key_ (Redis &gt;</a></h1> 1.3.10)=
<h1><a name="HGETALL _key_ (Redis &gt;">HGETALL _key_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(N), where N is the total number of entries</i><blockquote>HKEYS returns all the fields names contained into a hash, HVALS all the associated values, while HGETALL returns both the fields and values in the form of <i>field1</i>, <i>value1</i>, <i>field2</i>, <i>value2</i>, ..., <i>fieldN</i>, <i>valueN</i>.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Multi Bulk Reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HincrbyCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HINCRBY _key_ _field_ _value_ (Redis &gt;">HINCRBY _key_ _field_ _value_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Examples">Examples</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HincrbyCommand</h1>
<div class="summary">
</div>
<div class="narrow">
<h1><a name="HINCRBY _key_ _field_ _value_ (Redis &gt;">HINCRBY _key_ _field_ _value_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Increment the number stored at <i>field</i> in the hash at <i>key</i> by <i>value</i>. If <i>key</i> does not exist, a new key holding a hash is created. If <i>field</i> does not exist or holds a string, the value is set to 0 before applying the operation.</blockquote>
<blockquote>The range of values supported by HINCRBY is limited to 64 bit signed integers.</blockquote><h2><a name="Examples">Examples</a></h2>
Since the <i>value</i> argument is signed you can use this command to perform both increments and decrements:<br/><br/><pre class="codeblock python" name="code">
HINCRBY key field 1 (increment by one)
HINCRBY key field -1 (decrement by one, just like the DECR command)
HINCRBY key field -10 (decrement by 10)
</pre>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a> The new value at <i>field</i> after the increment operation.
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HlenCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HLEN _key_ (Redis &gt;">HLEN _key_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HlenCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HLEN _key_ (Redis &gt;">HLEN _key_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Return the number of entries (fields) contained in the hash stored at <i>key</i>. If the specified <i>key</i> does not exist, 0 is returned assuming an empty hash. </blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HmsetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HMSET _key_ _field1_ _value1_ ... _fieldN_ _valueN_ (Redis &gt;">HMSET _key_ _field1_ _value1_ ... _fieldN_ _valueN_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HmsetCommand</h1>
<div class="summary">
</div>
<div class="narrow">
<h1><a name="HMSET _key_ _field1_ _value1_ ... _fieldN_ _valueN_ (Redis &gt;">HMSET _key_ _field1_ _value1_ ... _fieldN_ _valueN_ (Redis &gt;</a></h1> 1.3.10) =
<i>Time complexity: O(N) (with N being the number of fields)</i><blockquote>Set the respective fields to the respective values. HMSET replaces old values with new values.</blockquote>
<blockquote>If <i>key</i> does not exist, a new key holding a hash is created.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a> Always +OK because HMSET can't fail
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HsetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HSET _key_ _field_ _value_ (Redis &gt;">HSET _key_ _field_ _value_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HsetCommand</h1>
<div class="summary">
</div>
<div class="narrow">
&iuml;&raquo;&iquest;#sidebar <a href="HashCommandsSidebar.html">HashCommandsSidebar</a><h1><a name="HSET _key_ _field_ _value_ (Redis &gt;">HSET _key_ _field_ _value_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Set the specified hash <i>field</i> to the specified <i>value</i>.</blockquote>
<blockquote>If <i>key</i> does not exist, a new key holding a hash is created.</blockquote>
<blockquote>If the field already exists, and the HSET just produced an update of thevalue, 0 is returned, otherwise if a new field is created 1 is returned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<link type="text/css" rel="stylesheet" href="style.css" />
</head>
<body>
<div id="page">
<div id='header'>
<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
</a>
</div>
<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>HsetnxCommand: Contents</b><br>&nbsp;&nbsp;<a href="#HSETNX _key_ _field_ _value_ (Redis &gt;">HSETNX _key_ _field_ _value_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
</div>
<h1 class="wikiname">HsetnxCommand</h1>
<div class="summary">
</div>
<div class="narrow">
<h1><a name="HSETNX _key_ _field_ _value_ (Redis &gt;">HSETNX _key_ _field_ _value_ (Redis &gt;</a></h1> 1.3.10)=
<i>Time complexity: O(1)</i><blockquote>Set the specified hash <i>field</i> to the specified <i>value</i>, if <i>field</i> does not exist yet.</blockquote>
<blockquote>If <i>key</i> does not exist, a new key holding a hash is created.</blockquote>
<blockquote>If the field already exists, this operation has no effect and returns 0.Otherwise, the field is set to <i>value</i> and the operation returns 1.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>
</div>
</div>
</div>
</body>
</html>
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment