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<b>QuitCommand: Contents</b><br>&nbsp;&nbsp;<a href="#Quit">Quit</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
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<h1><a name="Quit">Quit</a></h1><blockquote>Ask the server to silently close the connection.</blockquote>
<h2><a name="Return value">Return value</a></h2>None. The connection is closed as soon as the QUIT command is received.
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<b>README: Contents</b><br>&nbsp;&nbsp;<a href="#Introduction">Introduction</a><br>&nbsp;&nbsp;<a href="#Beyond key-value databases">Beyond key-value databases</a><br>&nbsp;&nbsp;<a href="#What are the differences between Redis and Memcached?">What are the differences between Redis and Memcached?</a><br>&nbsp;&nbsp;<a href="#What are the differences between Redis and Tokyo Cabinet / Tyrant?">What are the differences between Redis and Tokyo Cabinet / Tyrant?</a><br>&nbsp;&nbsp;<a href="#Does Redis support locking?">Does Redis support locking?</a><br>&nbsp;&nbsp;<a href="#Multiple databases support">Multiple databases support</a><br>&nbsp;&nbsp;<a href="#Redis Data Types">Redis Data Types</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Implementation Details">Implementation Details</a><br>&nbsp;&nbsp;<a href="#Redis Tutorial">Redis Tutorial</a><br>&nbsp;&nbsp;<a href="#License">License</a><br>&nbsp;&nbsp;<a href="#Credits">Credits</a>
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<h1 class="wikiname">README</h1>
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<h1><a name="Introduction">Introduction</a></h1>Redis is a database. To be specific, Redis is a very simple database implementing a dictionary, where every key is associated with a value. For example I can set the key &quot;surname_1992&quot; to the string &quot;Smith&quot;.
What makes Redis different from many other key-value stores, is that every single value has a type. The following types are supported:<br/><br/><ul><li> String</li><li> List</li><li> Set</li><li> Sorted Set (since version 1.1)</li></ul>
The type of a value determines what operations (called commands) are available for the value itself.
For example you can append elements to a list stored at the key &quot;mylist&quot; using the LPUSH or RPUSH command in O(1). Later you'll be able to get a range of elements with LRANGE or trim the list with LTRIM. Sets are very flexible too, it is possible to add and remove elements from Sets (unsorted collections of strings), and then ask for server-side intersection, union, difference of Sets. Each command is performed through server-side atomic operations.
Please refer to the <a href="CommandReference.html">Command Reference</a> to see the full list of operations associated to these data types.<br/><br/>In other words, you can look at Redis as a data structures server. A Redis user is virtually provided with an interface to <a href="http://en.wikipedia.org/wiki/Abstract_data_type" target="_blank">Abstract Data Types</a>, saving her from the responsibility to implement concrete data structures and algorithms. Indeed both algorithms and data structures in Redis are properly choosed in order to obtain the best performance.<br/><br/>Redis loads and mantains the whole dataset into memory, but the dataset is persistent, since from time to time Redis writes a dump on disk asynchronously. The dataset is loaded from the dump every time the server is (re)started.<br/><br/>Redis can be configured to save the dataset when a certain number of changes is reached and after a given number of seconds elapses. For example, you can configure Redis to save after 1000 changes and at most 60 seconds since the last save. You can specify any combination for these numbers.<br/><br/>Because data is written asynchronously, when a system crash occurs, the last few queries can get lost (that is acceptable in many applications). Anyway it is possible to make this a non issue, since Redis supports master-slave replication from its early days, being effective even in the case where a few records lost are not acceptable.<h1><a name="Beyond key-value databases">Beyond key-value databases</a></h1>All these features allow to use Redis as the sole DB for your scalable application without the need of any relational database. <a href="TwitterAlikeExample.html">We wrote a simple Twitter clone in PHP + Redis</a> to show a real world example, the link points to an article explaining the design and internals in very simple words.<h1><a name="What are the differences between Redis and Memcached?">What are the differences between Redis and Memcached?</a></h1>In the following ways:<br/><br/><ul><li> Memcached is not persistent, it just holds everything in memory without saving since its main goal is to be used as a cache. Redis instead can be used as the main DB for the application. We <a href="TwitterAlikeExample.html">wrote a simple Twitter clone</a> using only Redis as database.</li></ul>
<ul><li> Like memcached Redis uses a key-value model, but while keys can just be strings, values in Redis can be lists and sets, and complex operations like intersections, set/get n-th element of lists, pop/push of elements, can be performed against sets and lists. It is possible to use lists as message queues.</li></ul>
<h1><a name="What are the differences between Redis and Tokyo Cabinet / Tyrant?">What are the differences between Redis and Tokyo Cabinet / Tyrant?</a></h1>Redis and Tokyo Cabinet can be used for the same applications, but actually they are <b>very</b> different beasts. If you read twitter messages of people involved in scalable things both products are reported to work well, but surely there are times where one or the other can be the best choice. Some differences are the followings (I may be biased, make sure to check yourself both the products).<br/><br/><ul><li> Tokyo Cabinet writes synchronously on disk, Redis takes the whole dataset on memory and writes on disk asynchronously. Tokyo Cabinet is safer and probably a better idea if your dataset is going to be bigger than RAM, but Redis is faster (note that Redis supports master-slave replication that is trivial to setup, so you are safe anyway if you want a setup where data can't be lost even after a disaster).</li></ul>
<ul><li> Redis supports higher level operations and data structures. Tokyo Cabinet supports a kind of database that is able to organize data into rows with named fields (in a way very similar to Berkeley DB) but can't do things like server side List and Set operations Redis is able to do: pushing or popping from Lists in an atomic way, in O(1) time complexity, server side Set intersections, <a href="SORT.html">SortCommand</a> ing of schema free data in complex ways (Btw TC supports sorting in the table-based database format). Redis on the other hand does not support the abstraction of tables with fields, the idea is that you can build this stuff in software easily if you really need a table-alike approach.</li></ul>
<ul><li> Tokyo Cabinet does not implement a networking layer. You have to use a networking layer called Tokyo Tyrant that interfaces to Tokyo Cabinet so you can talk to Tokyo Cabinet in a client-server fashion. In Redis the networking support is built-in inside the server, and is basically the only interface between the external world and the dataset.</li></ul>
<ul><li> Redis is reported to be much faster, especially if you plan to access Tokyo Cabinet via Tokyo Tyrant. Here I can only say that with Redis you can expect 100,000 operations/seconds with a normal Linux box and 50 concurrent clients. You should test Redis, Tokyo, and the other alternatives with your specific work load to get a feeling about performances for your application.</li></ul>
<ul><li> Redis is (IMHO) generally an higher level and simpler to use beast in the operations supported, and to get started. <a href="Check.html">the command reference CommandReference</a> to get a feeling. You can even start playing with Redis by telnet after reading the five minutes tutorial at the end of this README file. To implement new client libraries is trivial. <a href="Check.html">the protocol specification ProtocolSpecification</a> for more information.</li></ul><blockquote></blockquote><ul><li> Redis is not an on-disk DB engine like Tokyo: the latter can be used as a fast DB engine in your C project without the networking overhead just linking to the library. Still in many scalable applications you need multiple servers talking with multiple clients, so the client-server model is almost always needed, this is why in Redis this is built-in.</li></ul>
<h1><a name="Does Redis support locking?">Does Redis support locking?</a></h1>No, the idea is to provide atomic primitives in order to make the programmer
able to use redis with locking free algorithms. For example imagine you have
10 computers and one Redis server. You want to count words in a very large text.
This large text is split among the 10 computers, every computer will process
its part and use Redis's INCR command to atomically increment a counter
for every occurrence of the word found.<br/><br/>INCR/DECR are not the only atomic primitives, there are others like PUSH/POP
on lists, POP RANDOM KEY operations, UPDATE and so on. For example you can
use Redis like a Tuple Space (<a href="http://en.wikipedia.org/wiki/Tuple_space" target="_blank">http://en.wikipedia.org/wiki/Tuple_space</a>) in
order to implement distributed algorithms.<br/><br/>(News: locking with key-granularity is now planned)<h1><a name="Multiple databases support">Multiple databases support</a></h1>Another synchronization primitive is the support for multiple DBs. By default DB 0 is selected for every new connection, but using the SELECT command it is possible to select a different database. The MOVE operation can move an item from one DB to another atomically. This can be used as a base for locking free algorithms together with the 'RANDOMKEY' commands.<h1><a name="Redis Data Types">Redis Data Types</a></h1>Redis supports the following three data types as values:<br/><br/><ul><li> Strings: just any sequence of bytes. Redis strings are binary safe so they can not just hold text, but images, compressed data and everything else.</li><li> Lists: lists of strings, with support for operations like append a new string on head, on tail, list length, obtain a range of elements, truncate the list to a given length, sort the list, and so on.</li><li> Sets: an unsorted set of strings. It is possible to add or delete elements from a set, to perform set intersection, union, subtraction, and so on.</li></ul>
Values can be Strings, Lists or Sets. Keys can be a subset of strings not containing newlines (&quot;\n&quot;) and spaces (&quot; &quot;).<br/><br/>Note that sometimes strings may hold numeric vaules that must be parsed by
Redis. An example is the INCR command that atomically increments the number
stored at the specified key. In this case Redis is able to handle integers
that can be stored inside a 'long long' type, that is a 64-bit signed integer.<h2><a name="Implementation Details">Implementation Details</a></h2>Strings are implemented as dynamically allocated strings of characters.
Lists are implemented as doubly linked lists with cached length.
Sets are implemented using hash tables that use chaining to resolve collisions.<h1><a name="Redis Tutorial">Redis Tutorial</a></h1>(note, you can skip this section if you are only interested in &quot;formal&quot; doc.)<br/><br/>Later in this document you can find detailed information about Redis commands,
the protocol specification, and so on. This kind of documentation is useful
but... if you are new to Redis it is also BORING! The Redis protocol is designed
so that is both pretty efficient to be parsed by computers, but simple enough
to be used by humans just poking around with the 'telnet' command, so this
section will show to the reader how to play a bit with Redis to get an initial
feeling about it, and how it works.<br/><br/>To start just compile redis with 'make' and start it with './redis-server'.
The server will start and log stuff on the standard output, if you want
it to log more edit redis.conf, set the loglevel to debug, and restart it.<br/><br/>You can specify a configuration file as unique parameter:<br/><br/><blockquote>./redis-server /etc/redis.conf</blockquote>
This is NOT required. The server will start even without a configuration file
using a default built-in configuration.<br/><br/>Now let's try to set a key to a given value:<br/><br/><pre class="codeblock python" name="code">
$ telnet localhost 6379
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
SET foo 3
bar
+OK
</pre>The first line we sent to the server is &quot;set foo 3&quot;. This means &quot;set the key
foo with the following three bytes I'll send you&quot;. The following line is
the &quot;bar&quot; string, that is, the three bytes. So the effect is to set the
key &quot;foo&quot; to the value &quot;bar&quot;. Very simple!<br/><br/>(note that you can send commands in lowercase and it will work anyway,
commands are not case sensitive)<br/><br/>Note that after the first and the second line we sent to the server there
is a newline at the end. The server expects commands terminated by &quot;\r\n&quot;
and sequence of bytes terminated by &quot;\r\n&quot;. This is a minimal overhead from
the point of view of both the server and client but allows us to play with
Redis with the telnet command easily.<br/><br/>The last line of the chat between server and client is &quot;+OK&quot;. This means
our key was added without problems. Actually SET can never fail but
the &quot;+OK&quot; sent lets us know that the server received everything and
the command was actually executed.<br/><br/>Let's try to get the key content now:<br/><br/><pre class="codeblock python python" name="code">
GET foo
$3
bar
</pre>Ok that's very similar to 'set', just the other way around. We sent &quot;get foo&quot;,
the server replied with a first line that is just the $ character follwed by
the number of bytes the value stored at key contained, followed by the actual
bytes. Again &quot;\r\n&quot; are appended both to the bytes count and the actual data. In Redis slang this is called a bulk reply.<br/><br/>What about requesting a non existing key?<br/><br/><pre class="codeblock python python python" name="code">
GET blabla
$-1
</pre>When the key does not exist instead of the length, just the &quot;$-1&quot; string is sent. Since a -1 length of a bulk reply has no meaning it is used in order to specifiy a 'nil' value and distinguish it from a zero length value. Another way to check if a given key exists or not is indeed the EXISTS command:<br/><br/><pre class="codeblock python python python python" name="code">
EXISTS nokey
:0
EXISTS foo
:1
</pre>As you can see the server replied ':0' the first time since 'nokey' does not
exist, and ':1' for 'foo', a key that actually exists. Replies starting with the colon character are integer reply.<br/><br/>Ok... now you know the basics, read the <a href="CommandReference.html">REDIS COMMAND REFERENCE</a> section to
learn all the commands supported by Redis and the <a href="ProtocolSpecification.html">PROTOCOL SPECIFICATION</a>
section for more details about the protocol used if you plan to implement one
for a language missing a decent client implementation.<h1><a name="License">License</a></h1>Redis is released under the BSD license. See the COPYING file for more information.<h1><a name="Credits">Credits</a></h1>Redis is written and maintained by Salvatore Sanfilippo, Aka 'antirez'.<br/><br/>Enjoy,
antirez
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<b>RandomkeyCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RANDOMKEY">RANDOMKEY</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="RANDOMKEY">RANDOMKEY</a></h1>
<i>Time complexity: O(1)</i><blockquote>Return a randomly selected key from the currently selected DB.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Singe line reply</a>, specifically the randomly selected key or an empty string is the database is empty.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="KeysCommand.html">KEYS</a></li></ul>
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<b>Redis0100ChangeLog: Contents</b><br>&nbsp;&nbsp;<a href="#Redis 0.100 Changelog">Redis 0.100 Changelog</a>
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<h1><a name="Redis 0.100 Changelog">Redis 0.100 Changelog</a></h1>
<pre class="codeblock python" name="code">
- SUNION, SDIFF, SUNIONSTORE, SDIFFSTORE commands implemented. (Aman Gupta, antirez)
- Non blocking replication. Now while N slaves are synchronizing, the master will continue to ask to client queries. (antirez)
- PHP client ported to PHP5 (antirez)
- FLUSHALL/FLUSHDB no longer sync on disk. Just increment the dirty counter by the number of elements removed, that will probably trigger a background saving operation (antirez)
- INCRBY/DECRBY now support 64bit increments, with tests (antirez)
- New fields in INFO command, bgsave_in_progress and replication related (antirez)
- Ability to specify a different file name for the DB (... can't remember ...)
- GETSET command, atomic GET + SET (antirez)
- SMOVE command implemented, atomic move-element across sets operation (antirez)
- Ability to work with huge data sets, tested up to 350 million keys (antirez)
- Warns if /proc/sys/vm/overcommit_memory is set to 0 on Linux. Also make sure to don't resize the hash tables while the child process is saving in order to avoid copy-on-write of memory pages (antirez)
- Infinite number of arguments for MGET and all the other commands (antirez)
- CPP client (Brian Hammond)
- DEL is now a vararg, IMPORTANT: memory leak fixed in loading DB code (antirez)
- Benchmark utility now supports random keys (antirez)
- Timestamp in log lines (antirez)
- Fix SINTER/UNIONSTORE to allow for &amp;=/|= style operations (i.e. SINTERSTORE set1 set1 set2) (Aman Gupta)
- Partial qsort implemented in SORT command, only when both BY and LIMIT is used (antirez)
- Allow timeout=0 config to disable client timeouts (Aman Gupta)
- Alternative (faster/simpler) ruby client API compatible with Redis-rb (antirez)
- S*STORE now return the cardinality of the resulting set (antirez)
- TTL command implemented (antirez)
- Critical bug about glueoutputbuffers=yes fixed. Under load and with pipelining and clients disconnecting on the middle of the chat with the server, Redis could block. (antirez)
- Different replication fixes (antirez)
- SLAVEOF command implemented for remote replication management (antirez)
- Issue with redis-client used in scripts solved, now to check if the latest argument must come from standard input we do not check that stdin is or not a tty but the command arity (antirez)
- Warns if using the default config (antirez)
- maxclients implemented, see redis.conf for details (antirez)
- max bytes of a received command enlarged from 1k to 32k (antirez)
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<b>Redis0900ChangeLog: Contents</b><br>&nbsp;&nbsp;<a href="#CHANGELOG for Redis 0.900">CHANGELOG for Redis 0.900</a>
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<h1><a name="CHANGELOG for Redis 0.900">CHANGELOG for Redis 0.900</a></h1><pre class="codeblock python" name="code">
2009-06-16 client libraries updated (antirez)
2009-06-16 Better handling of background saving process killed or crashed (antirez)
2009-06-14 number of keys info in INFO command (Diego Rosario Brogna)
2009-06-14 SPOP documented (antirez)
2009-06-14 Clojure library (Ragnar Dahl&Atilde;&copy;n)
2009-06-10 It is now possible to specify - as config file name to read it from stdin (antirez)
2009-06-10 max bytes in an inline command raised to 1024*1024 bytes, in order to allow for very large MGETs and still protect from client crashes (antirez)
2009-06-08 SPOP implemented. Hash table resizing for Sets and Expires too. Changed the resize policy to play better with RANDOMKEY and SPOP. (antirez)
2009-06-07 some minor changes to the backtrace code (antirez)
2009-06-07 enable backtrace capabilities only for Linux and MacOSX (antirez)
2009-06-07 Dump a backtrace on sigsegv/sigbus, original coded (Diego Rosario Brogna)
2009-06-05 Avoid a busy loop while sending very large replies against very fast links, this allows to be more responsive with other clients even under a KEY * against the loopback interface (antirez)
2009-06-05 Kill the background saving process before performing SHUTDOWN to avoid races (antirez)
2009-06-05 LREM now returns :0 for non existing keys (antirez)
2009-06-05 added config.h for #ifdef business isolation, added fstat64 for Mac OS X (antirez)
2009-06-04 macosx specific zmalloc.c, uses malloc_size function in order to avoid to waste memory and time to put an additional header (antirez)
2009-06-04 DEBUG OBJECT implemented (antirez)
2009-06-03 shareobjectspoolsize implemented in reds.conf, in order to control the pool size when object sharing is on (antirez)
2009-05-27 maxmemory implemented (antirez)
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<b>RenameCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RENAME _oldkey_ _newkey_">RENAME _oldkey_ _newkey_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="RENAME _oldkey_ _newkey_">RENAME _oldkey_ _newkey_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Atomically renames the key <i>oldkey</i> to <i>newkey</i>. If the source anddestination name are the same an error is returned. If <i>newkey</i>already exists it is overwritten.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code repy</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RenamenxCommand.html">RENAMENX</a> if you don't want overwrite the destination key if it exists.</li></ul>
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<b>RenamenxCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RENAMENX _oldkey_ _newkey_">RENAMENX _oldkey_ _newkey_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="RENAMENX _oldkey_ _newkey_">RENAMENX _oldkey_ _newkey_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Rename <i>oldkey</i> into <i>newkey</i> but fails if the destination key <i>newkey</i> already exists.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
1 if the key was renamed
0 if the target key already exist
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RenameCommand.html">RENAME</a> is like RENAMENX but overwrite existing destionation key.</li></ul>
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<b>ReplicationHowto: Contents</b><br>&nbsp;&nbsp;<a href="#Redis Replication Howto">Redis Replication Howto</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#General Information">General Information</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#How Redis replication works">How Redis replication works</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Configuration">Configuration</a>
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<h1><a name="Redis Replication Howto">Redis Replication Howto</a></h1><h2><a name="General Information">General Information</a></h2>Redis replication is a very simple to use and configure master-slave replication that allows slave Redis servers to be exact copies of master servers. The following are some very important facts about Redis replication:<br/><br/><ul><li> A master can have multiple slaves.</li><li> Slaves are able to accept other slaves connections, so instead to connect a number of slaves against the same master it is also possible to connect some of the slaves to other slaves in a graph-alike structure.</li><li> Redis replication is non-blocking on the master side, this means that the master will continue to serve queries while one or more slaves are performing the first synchronization. Instead replication is blocking on the slave side: while the slave is performing the first synchronization it can't reply to queries.</li><li> Replications can be used both for scalability, in order to have multiple slaves for read-only queries (for example heavy <a href="SortCommand.html">SORT</a> operations can be launched against slaves), or simply for data redundancy.</li><li> It is possible to use replication to avoid the saving process on the master side: just configure your master redis.conf in order to avoid saving at all (just comment al the &quot;save&quot; directives), then connect a slave configured to save from time to time.</li></ul>
<h2><a name="How Redis replication works">How Redis replication works</a></h2>In order to start the replication, or after the connection closes in order resynchronize with the master, the client connects to the master and issues the SYNC command.<br/><br/>The master starts a background saving, and at the same time starts to collect all the new commands received that had the effect to modify the dataset. When the background saving completed the master starts the transfer of the database file to the slave, that saves it on disk, and then load it in memory. At this point the master starts to send all the accumulated commands, and all the new commands received from clients, that had the effect of a dataset modification.<br/><br/>You can try it yourself via telnet. Connect to the Redis port while the server is doing some work and issue the SYNC command. You'll see a bulk transfer and then every command received by the master will be re-issued in the telnet session.<br/><br/>Slaves are able to automatically reconnect when the master <code name="code" class="python">&lt;-&gt;</code> slave link goes down for some reason. If the master receives multiple concurrent slave synchronization requests it performs a single background saving in order to serve all them.<h2><a name="Configuration">Configuration</a></h2>To configure replication is trivial: just add the following line to the slave configuration file:
<pre class="codeblock python" name="code">
slaveof 192.168.1.1 6379
</pre>
Of course you need to replace 192.168.1.1 6379 with your master ip address (or hostname) and port.
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<b>ReplyTypes: Contents</b><br>&nbsp;&nbsp;<a href="#Redis Reply Types">Redis Reply Types</a><br>&nbsp;&nbsp;<a href="#Status code reply">Status code reply</a><br>&nbsp;&nbsp;<a href="#Error reply">Error reply</a><br>&nbsp;&nbsp;<a href="#Integer reply">Integer reply</a><br>&nbsp;&nbsp;<a href="#Bulk reply">Bulk reply</a><br>&nbsp;&nbsp;<a href="#Multi bulk reply">Multi bulk reply</a>
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<h1><a name="Redis Reply Types">Redis Reply Types</a></h1>Redis commands can reply to the client with four different kind of replies, you can find the protocol level specification of this replies in the <a href="ProtocolSpecification.html">Redis Protocol Specification</a>. This page is instead an higher level description of the four types of replies from the point of view of the final user.<h1><a name="Status code reply">Status code reply</a></h1>
Status code replies are single line strings having the <b>+</b> character as first byte. The string to return to the client is simply verything that follows the first <b>+</b> character. For example the <a href="PingCommand.html">PING</a> command returns <b>+PONG</b>, that is the string &quot;PONG&quot;.<h1><a name="Error reply">Error reply</a></h1>
This is like a status code reply but the first character is <b>-</b> instead of <b>+</b>. The client library should raise an error for error replies and stop the execution of the program if the exception is not trapped, showing the error message (everything following the first <b>-</b> character). An example of error is &quot;-Error no such key&quot; or &quot;-foobar&quot;. Note that error replies will not collide with negative integer replies since integer replies are prefixed with the <b>:</b> character.<h1><a name="Integer reply">Integer reply</a></h1>
At protocol level integer replies are single line replies in form of a decimal singed number prefixed by a <b>:</b> character. For example <b>:10</b> is an integer reply. Redis commands returning <i>true</i> or <i>false</i> will use an integer reply with 0 or 1 as values where 0 is false and 1 is true.<br/><br/>Integer replies are usually passed by client libraries as integer values.<h1><a name="Bulk reply">Bulk reply</a></h1>
A bulk reply is a binary-safe reply that is used to return a binary safe single string value (string is not limited to alphanumerical strings, it may contain binary data of any kind). Client libraries will usually return a string as return value of Redis commands returning bulk replies. There is a special bulk reply that signal that the element does not exist. When this happens the client library should return 'nil', 'false', or some other special element that can be distinguished by an empty string.<h1><a name="Multi bulk reply">Multi bulk reply</a></h1>
While a bulk reply returns a single string value, multi bulk replies are used to return multiple values: lists, sets, and so on. Elements of a bulk reply can be missing. Client libraries should return 'nil' or 'false' in order to make this elements distinguishable from empty strings. Client libraries should return multi bulk replies that are about ordered elements like list ranges as lists, and bulk replies about sets as hashes or Sets if the implementation language has a Set type.
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<b>RoadMap: Contents</b><br>&nbsp;&nbsp;<a href="#Road Map (ROUGH DRAFT)">Road Map (ROUGH DRAFT)</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#TODO">TODO</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#1.2">1.2</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#1.1">1.1</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#1.0">1.0</a>
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<h1><a name="Road Map (ROUGH DRAFT)">Road Map (ROUGH DRAFT)</a></h1>The up to date, raw Road Map for Redis is part of the source code, you can find it here: <a href="http://github.com/antirez/redis/raw/master/TODO" target="_blank">http://github.com/antirez/redis/raw/master/TODO</a><h2><a name="TODO">TODO</a></h2>Add this information:<br/><br/><a href="http://groups.google.com/group/redis-db/browse_thread/thread/95329fcbf7825169/70214fc6cfe01856?lnk=gst&q=roadmap#70214fc6cfe01856" target="_blank">http://groups.google.com/group/redis-db/browse_thread/thread/95329fcbf7825169/70214fc6cfe01856?lnk=gst&amp;q=roadmap#70214fc6cfe01856</a><h2><a name="1.2">1.2</a></h2> <br/><br/><ul><li> <a href="DataTypes.html">Hash data type</a>.</li></ul><blockquote></blockquote><h2><a name="1.1">1.1</a></h2><ul><li> <a href="DataTypes.html">Ordered Set (ZSET)</a></li><li> <a href="MultiBulkCommands.html">Multibulk Commands</a></li><li> In memory integer encoding of <a href="DataTypes.html">integers</a>. Memory saving of 20% or more with datasets using high number of integer IDs. </li><li> Enhanced <a href="ExpireCommand.html">EXPIRE</a> algorithm.</li></ul>
<h2><a name="1.0">1.0</a></h2><ul><li> TODO: Add 1.0 Features. This is important for clarity in <a href="SupportedLanguages.html">SupportedLanguages</a> </li></ul>
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<b>RpoplpushCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RPOPLPUSH _srckey_ _dstkey_ (Redis &gt;">RPOPLPUSH _srckey_ _dstkey_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Programming patterns: safe queues">Programming patterns: safe queues</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Programming patterns: server-side O(N) list traversal">Programming patterns: server-side O(N) list traversal</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="RPOPLPUSH _srckey_ _dstkey_ (Redis &gt;">RPOPLPUSH _srckey_ _dstkey_ (Redis &gt;</a></h1> 1.1) =
<i>Time complexity: O(1)</i><blockquote>Atomically return and remove the last (tail) element of the <i>srckey</i> list,and push the element as the first (head) element of the <i>dstkey</i> list. Forexample if the source list contains the elements &quot;a&quot;,&quot;b&quot;,&quot;c&quot; and thedestination list contains the elements &quot;foo&quot;,&quot;bar&quot; after an RPOPLPUSH commandthe content of the two lists will be &quot;a&quot;,&quot;b&quot; and &quot;c&quot;,&quot;foo&quot;,&quot;bar&quot;.</blockquote>
<blockquote>If the <i>key</i> does not exist or the list is already empty the specialvalue 'nil' is returned. If the <i>srckey</i> and <i>dstkey</i> are the same theoperation is equivalent to removing the last element from the list and pusingit as first element of the list, so it's a &quot;list rotation&quot; command.</blockquote>
<h2><a name="Programming patterns: safe queues">Programming patterns: safe queues</a></h2><blockquote>Redis lists are often used as queues in order to exchange messages betweendifferent programs. A program can add a message performing an <a href="RpushCommand.html">LPUSH</a> operationagainst a Redis list (we call this program a Producer), while another program(that we call Consumer) can process the messages performing an <a href="LpopCommand.html">RPOP</a> commandin order to start reading the messages from the oldest.</blockquote>
<blockquote>Unfortunately if a Consumer crashes just after an <a href="LpopCommand.html">RPOP</a> operation the messagegets lost. RPOPLPUSH solves this problem since the returned message isadded to another &quot;backup&quot; list. The Consumer can later remove the messagefrom the backup list using the <a href="LremCommand.html">LREM</a> command when the message was correctlyprocessed.</blockquote>
<blockquote>Another process, called Helper, can monitor the &quot;backup&quot; list to check fortimed out entries to repush against the main queue.</blockquote>
<h2><a name="Programming patterns: server-side O(N) list traversal">Programming patterns: server-side O(N) list traversal</a></h2><blockquote>Using RPOPPUSH with the same source and destination key a process canvisit all the elements of an N-elements List in O(N) without to transferthe full list from the server to the client in a single <a href="LrangeCommand.html">LRANGE</a> operation.Note that a process can traverse the list even while other processesare actively RPUSHing against the list, and still no element will be skipped.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RpushCommand.html">RPUSH</a></li><li> <a href="RpushCommand.html">LPUSH</a></li><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li><li> <a href="LremCommand.html">LREM</a></li><li> <a href="LpopCommand.html">LPOP</a></li><li> <a href="LpopCommand.html">RPOP</a></li><li> <a href="RpoplpushCommand.html">RPOPLPUSH</a></li></ul>
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<b>RpushCommand: Contents</b><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#RPUSH _key_ _string_">RPUSH _key_ _string_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#LPUSH _key_ _string_">LPUSH _key_ _string_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h3><a name="RPUSH _key_ _string_">RPUSH _key_ _string_</a></h3>
<h3><a name="LPUSH _key_ _string_">LPUSH _key_ _string_</a></h3>
<i>Time complexity: O(1)</i><blockquote>Add the <i>string</i> value to the head (RPUSH) or tail (LPUSH) of the liststored at <i>key</i>. If the key does not exist an empty list is created just beforethe append operation. If the key exists but is not a List an erroris returned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RpushCommand.html">RPUSH</a></li><li> <a href="RpushCommand.html">LPUSH</a></li><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li><li> <a href="LremCommand.html">LREM</a></li><li> <a href="LpopCommand.html">LPOP</a></li><li> <a href="LpopCommand.html">RPOP</a></li><li> <a href="RpoplpushCommand.html">RPOPLPUSH</a></li></ul>
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<b>SaddCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SADD _key_ _member_">SADD _key_ _member_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="SADD _key_ _member_">SADD _key_ _member_</a></h1>
<i>Time complexity O(1)</i><blockquote>Add the specified <i>member</i> to the set value stored at <i>key</i>. If <i>member</i>is already a member of the set no operation is performed. If <i>key</i>does not exist a new set with the specified <i>member</i> as sole member iscrated. If the key exists but does not hold a set value an error isreturned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
1 if the new element was added
0 if the element was already a member of the set
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SremCommand.html">SREM</a></li><li> <a href="SismemberCommand.html">SISMEMBER</a></li><li> <a href="ScardCommand.html">SCARD</a></li><li> <a href="SmembersCommand.html">SMEMBERS</a></li><li> <a href="SinterCommand.html">SINTER</a></li><li> <a href="SinterstoreCommand.html">SINTERSTORE</a></li><li> <a href="SmoveCommand.html">SMOVE</a></li></ul>
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<b>SaveCommand: Contents</b><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#SAVE">SAVE</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">SaveCommand</h1>
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<h3><a name="SAVE">SAVE</a></h3>
<blockquote>Save the DB on disk. The server hangs while the saving is notcompleted, no connection is served in the meanwhile. An OK codeis returned when the DB was fully stored in disk.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="BgsaveCommand.html">BGSAVE</a></li><li> <a href="ShutdownCommand.html">SHUTDOWN</a></li></ul>
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<b>ScardCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SCARD _key_">SCARD _key_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="SCARD _key_">SCARD _key_</a></h1>
<i>Time complexity O(1)</i><blockquote>Return the set cardinality (number of elements). If the <i>key</i> does notexist 0 is returned, like for empty sets.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
the cardinality (number of elements) of the set as an integer.
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SaddCommand.html">SADD</a></li><li> <a href="SremCommand.html">SREM</a></li><li> <a href="SismemberCommand.html">SISMEMBER</a></li><li> <a href="ScardCommand.html">SCARD</a></li><li> <a href="SmembersCommand.html">SMEMBERS</a></li><li> <a href="SinterCommand.html">SINTER</a></li><li> <a href="SinterstoreCommand.html">SINTERSTORE</a></li><li> <a href="SmoveCommand.html">SMOVE</a></li></ul>
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<b>SdiffCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SDIFF _key1_ _key2_ ... _keyN_">SDIFF _key1_ _key2_ ... _keyN_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="SDIFF _key1_ _key2_ ... _keyN_">SDIFF _key1_ _key2_ ... _keyN_</a></h1>
<i>Time complexity O(N) with N being the total number of elements of all the sets</i><blockquote>Return the members of a set resulting from the difference between the firstset provided and all the successive sets. Example:</blockquote>
<pre class="codeblock python" name="code">
key1 = x,a,b,c
key2 = c
key3 = a,d
SDIFF key1,key2,key3 =&gt; x,b
</pre><blockquote>Non existing keys are considered like empty sets.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Multi bulk reply</a>, specifically the list of common elements.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="SdiffstoreCommand.html">SDIFFSTORE</a></li><li> <a href="SaddCommand.html">SADD</a></li><li> <a href="SremCommand.html">SREM</a></li><li> <a href="SismemberCommand.html">SISMEMBER</a></li><li> <a href="ScardCommand.html">SCARD</a></li><li> <a href="SmembersCommand.html">SMEMBERS</a></li><li> <a href="SinterstoreCommand.html">SINTERSTORE</a></li><li> <a href="SunionCommand.html">SUNION</a></li><li> <a href="SunionstoreCommand.html">SUNIONSTORE</a></li><li> <a href="SmoveCommand.html">SMOVE</a></li></ul>
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<b>SdiffstoreCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SDIFFSTORE _dstkey_ _key1_ _key2_ ... _keyN_">SDIFFSTORE _dstkey_ _key1_ _key2_ ... _keyN_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">SdiffstoreCommand</h1>
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<h1><a name="SDIFFSTORE _dstkey_ _key1_ _key2_ ... _keyN_">SDIFFSTORE _dstkey_ _key1_ _key2_ ... _keyN_</a></h1>
<i>Time complexity O(N) where N is the total number of elements in all the provided sets</i><blockquote>This commnad works exactly like SDIFF but instead of being returned the resulting set is sotred in <i>dstkey</i>.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SdiffCommand.html">SDIFF</a></li><li> <a href="SremCommand.html">SREM</a></li><li> <a href="SismemberCommand.html">SISMEMBER</a></li><li> <a href="ScardCommand.html">SCARD</a></li><li> <a href="SmembersCommand.html">SMEMBERS</a></li><li> <a href="SinterCommand.html">SINTER</a></li><li> <a href="SinterstoreCommand.html">SINTERSTORE</a></li><li> <a href="SunionCommand.html">SUNION</a></li><li> <a href="SmoveCommand.html">SMOVE</a></li></ul>
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<b>SelectCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SELECT _index_">SELECT _index_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">SelectCommand</h1>
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<h1><a name="SELECT _index_">SELECT _index_</a></h1>
<blockquote>Select the DB with having the specified zero-based numeric index.For default every new client connection is automatically selectedto DB 0.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="FlushdbCommand.html">FLUSHDB</a></li><li> <a href="MoveCommand.html">MOVE</a></li></ul>
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<b>SetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SET _key_ _value_">SET _key_ _value_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">SetCommand</h1>
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<h1><a name="SET _key_ _value_">SET _key_ _value_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Set the string <i>value</i> as value of the <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">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SetnxCommand.html">SETNX</a> is like SET but don't perform the operation if the target key already exists.</li></ul>
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<h1 class="wikiname">SetnxCommand</h1>
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<h1><a name="SETNX _key_ _value_">SETNX _key_ _value_</a></h1>
<i>Time complexity: O(1)</i><blockquote>SETNX works exactly like <a href="SetCommand.html">SET</a> with the only difference thatif the key already exists no operation is performed.SETNX actually means &quot;SET if Not eXists&quot;.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
1 if the key was set
0 if the key was not set
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SetCommand.html">SET</a></li></ul>
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