Commit fc879abe authored by antirez's avatar antirez
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Merge branch 'unstable'

parents e4f6b8c3 cf1eefa4
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<b>RedisPipelining: Contents</b><br>&nbsp;&nbsp;<a href="#Request/Response protocols and RTT">Request/Response protocols and RTT</a><br>&nbsp;&nbsp;<a href="#Redis Pipelining">Redis Pipelining</a><br>&nbsp;&nbsp;<a href="#Some benchmark">Some benchmark</a><br>&nbsp;&nbsp;<a href="#Pipelining VS other multi-commands">Pipelining VS other multi-commands</a>
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<h1 class="wikiname">RedisPipelining</h1>
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<h1><a name="Request/Response protocols and RTT">Request/Response protocols and RTT</a></h1>
Redis is a TCP server using the client-server model and what is called a <b>Request/Response</b> protocol.<br/><br/>This means that usually a request is accomplished with the following steps:
<ul><li> The client sends a query to the server, and reads from the socket, usually in a blocking way, for the server response.</li><li> The server processes the command and sends the response back to the server.</li></ul>So for instance a four commands sequence is something like this:
<ul><li> <b>Client:</b> INCR X</li><li> <b>Server:</b> 1</li><li> <b>Client:</b> INCR X</li><li> <b>Server:</b> 2</li><li> <b>Client:</b> INCR X</li><li> <b>Server:</b> 3</li><li> <b>Client:</b> INCR X</li><li> <b>Server:</b> 4</li></ul>Clients and Servers are connected via a networking link. Such a link can be very fast (a loopback interface) or very slow (a connection established over the internet with many hops between the two hosts). Whatever the network latency is, there is a time for the packets to travel from the client to the server, and back from the server to the client to carry the reply.<br/><br/>This time is called RTT (Round Trip Time). It is very easy to see how this can affect the performances when a client needs to perform many requests in a row (for instance adding many elements to the same list, or populating a database with many keys). For instance if the RTT time is 250 milliseconds (in the case of a very slow link over the internet), even if the server is able to process 100k requests per second, we'll be able to process at max four requests per second.<br/><br/>If the interface used is a loopback interface, the RTT is much shorter (for instance my host reports 0,044 milliseconds pinging 127.0.0.1), but it is still a lot if you need to perform many writes in a row.<br/><br/>Fortunately there is a way to improve this use cases.
<h1><a name="Redis Pipelining">Redis Pipelining</a></h1>
A Request/Response server can be implemented so that it is able to process new requests even if the client didn't already read the old responses. This way it is possible to send <b>multiple commands</b> to the server without waiting for the replies at all, and finally read the replies in a single step.<br/><br/>This is called pipelining, and is a technique widely in use since many decades. For instance many POP3 protocol implementations already supported this feature, dramatically speeding up the process of downloading new emails from the server.<br/><br/>Redis supports pipelining since the very early days, so whatever version you are running, you can use pipelining with Redis. This is an example using the raw netcat utility:
<pre class="codeblock python" name="code">
$ (echo -en &quot;PING\r\nPING\r\nPING\r\n&quot;; sleep 1) | nc localhost 6379
+PONG
+PONG
+PONG
</pre>
This time we are not paying the cost of RTT for every call, but just one time for the three commands.<br/><br/>To be very explicit, with pipelining the order of operations of our very first example will be the following:
<ul><li> <b>Client:</b> INCR X</li><li> <b>Client:</b> INCR X</li><li> <b>Client:</b> INCR X</li><li> <b>Client:</b> INCR X</li><li> <b>Server:</b> 1</li><li> <b>Server:</b> 2</li><li> <b>Server:</b> 3</li><li> <b>Server:</b> 4</li></ul><b>IMPORTANT NOTE</b>: while the client sends commands using pipelining, the server will be forced to queue the replies, using memory. So if you need to send many many commands with pipelining it's better to send this commands up to a given reasonable number, for instance 10k commands, read the replies, and send again other 10k commands and so forth. The speed will be nearly the same, but the additional memory used will be at max the amount needed to queue the replies for this 10k commands.
<h1><a name="Some benchmark">Some benchmark</a></h1>
In the following benchmark we'll use the Redis Ruby client, supporting pipelining, to test the speed improvement due to pipelining:
<pre class="codeblock python python" name="code">
require 'rubygems'
require 'redis'
def bench(descr)
start = Time.now
yield
puts &quot;#{descr} #{Time.now-start} seconds&quot;
end
def without_pipelining
r = Redis.new
10000.times {
r.ping
}
end
def with_pipelining
r = Redis.new
r.pipelined {
10000.times {
r.ping
}
}
end
bench(&quot;without pipelining&quot;) {
without_pipelining
}
bench(&quot;with pipelining&quot;) {
with_pipelining
}
</pre>
Running the above simple script will provide this figures in my Mac OS X system, running over the loopback interface, where pipelining will provide the smallest improvement as the RTT is already pretty low:
<pre class="codeblock python python python" name="code">
without pipelining 1.185238 seconds
with pipelining 0.250783 seconds
</pre>
As you can see using pipelining we improved the transfer by a factor of five.
<h1><a name="Pipelining VS other multi-commands">Pipelining VS other multi-commands</a></h1>
Often we get requests about adding new commands performing multiple operations in a single pass.
For instance there is no command to add multiple elements in a set. You need calling many times SADD.<br/><br/>With pipelining you can have performances near to an MSADD command, but at the same time we'll avoid bloating the Redis command set with too many commands. An additional advantage is that the version written using just SADD will be ready for a distributed environment (for instance Redis Cluster, that is in the process of being developed) just dropping the pipelining code.
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<b>RedisStatus: Contents</b><br>&nbsp;&nbsp;<a href="#Redis Status Page">Redis Status Page</a><br>&nbsp;&nbsp;<a href="#How stable are the alpha previews?">How stable are the alpha previews?</a><br>&nbsp;&nbsp;<a href="#How to obtain a 2.2-alpha preview">How to obtain a 2.2-alpha preview</a><br>&nbsp;&nbsp;<a href="#ETA for Redis 2.2?">ETA for Redis 2.2?</a><br>&nbsp;&nbsp;<a href="#When will we be able to see a working version of Redis Cluster?">When will we be able to see a working version of Redis Cluster?</a>
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<h1 class="wikiname">RedisStatus</h1>
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<h1><a name="Redis Status Page">Redis Status Page</a></h1>Hello! Redis uses versions composed of three numbers separated by a dot: <b>major</b>.<b>minor</b>.<b>patchlevel</b>.<br/><br/>When the <b>minor</b> is an odd number, it is used for an unstable release, so stable releases are for instance 1.2, 2.0, and so forth.<br/><br/>This is the status of the different Redis versions currently available:<br/><br/><ul><li> 1.2 is the <b>legacy redis stable release</b>, now it is completely obsoleted by Redis 2.0. Redis 2.0 is almost completely back compatible with 1.2 so upgrading is usually not a problem. Still 1.2 is believed to be a very stable release that works well, so if you are using it in production with code that probably will not modified to use more advanced Redis features available in 2.0, it makes sense to take 1.2 running. For everything new, it's better to start with 2.0.</li></ul>
<ul><li> 2.0 is the current <b>stable release</b>. It is better than 1.2 in more or less everything: more features, more mature code, better replication, better persistence, and so forth. It is currently what most users should use, unless they really need features that are only available into an <b>unstable</b> release.</li></ul>
<ul><li> 2.1 is the current <b>unstable release</b>, and there are no tar.gz for this release, you need to download it from git. <b>Warning:</b> the master branch in git may work most of the time but is NOT what you should use. What's better instead is to use the 2.2-alpha tags: every time Redis 2.1.x is stable enough and the new features merged passed all the tests for a couple of weeks, and we didn't received severe bug reports from users, we tag master as 2.2-alpha <i>number</i>, where <i>number</i> is simply a progressive number. Just pick this number.</li></ul>
<h1><a name="How stable are the alpha previews?">How stable are the alpha previews?</a></h1>
Well it is surely ok for development, but it is not recommended for production. Still there are many users that trust Redis development process so much to use alpha releases in production, but this is up to you, we don't give any guarantee ;)<h1><a name="How to obtain a 2.2-alpha preview">How to obtain a 2.2-alpha preview</a></h1>Simply using git:
<pre class="codeblock python" name="code">
$ git clone git://github.com/antirez/redis.git
Initialized empty Git repository in /tmp/redis/.git/
...
</pre>
Then you can list all the branches matching 2.1-alpha with:
<pre class="codeblock python python" name="code">
cd redis
$ git tag | grep 2.2-alpha
2.2-alpha0
2.2-alpha1
2.2-alpha2
</pre>
At this point you can just use <b>git checkout <i>tagname</i></b>, substituting <i>tagname</i> with 2.2-alphaX where X is the greater progressive number you see in the listing.<h1><a name="ETA for Redis 2.2?">ETA for Redis 2.2?</a></h1>
Redis 2.2 is planned to enter the release candidate stage before the end of the 2010.<h1><a name="When will we be able to see a working version of Redis Cluster?">When will we be able to see a working version of Redis Cluster?</a></h1>
I'm already working at it, I mean not just designing, but writing code. In three months we should have some kind of experimental version, while in six months we should have the first release candidate.<br/><br/>Probably the first <b>stable</b> release of Redis with working cluster will be called 3.0, but I'll try to merge it into 2.2 as an experimental support if we'll be sure there is no impact in the stability of the system when clustering is not used.
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<b>Redis_1_2_0_Changelog: Contents</b><br>&nbsp;&nbsp;<a href="#What's new in Redis 1.2">What's new in Redis 1.2</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#New persistence mode: Append Only File">New persistence mode: Append Only File</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#New data type: sorted sets">New data type: sorted sets</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Specialized integer objects encoding">Specialized integer objects encoding</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#MSET and MSETNX">MSET and MSETNX</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Better Performances">Better Performances</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Solaris Support">Solaris Support</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Support for the new generation protocol">Support for the new generation protocol</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#A few new commands about already supported data types">A few new commands about already supported data types</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Bug fixing">Bug fixing</a><br>&nbsp;&nbsp;<a href="#CHANGELOG for Redis 1.1.90">CHANGELOG for Redis 1.1.90</a>
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<h1 class="wikiname">Redis_1_2_0_Changelog</h1>
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<h1><a name="What's new in Redis 1.2">What's new in Redis 1.2</a></h1><h2><a name="New persistence mode: Append Only File">New persistence mode: Append Only File</a></h2>The Append Only File is an alternative way to save your data in Redis that is fully durable! Unlike the snapshotting (default) persistence mode, where the database is saved asynchronously from time to time, the Append Only File saves every change ASAP in a text-only file that works like a journal. Redis will play back this file again at startup reloading the whole dataset back in memory. Redis Append Only File supports background Log compaction. For more info read the <a href="AppendOnlyFileHowto.html">Append Only File HOWTO</a>.<h2><a name="New data type: sorted sets">New data type: sorted sets</a></h2>Sorted sets are collections of elements (like Sets) with an associated score (in the form of a double precision floating point number). Elements in a sorted set are taken in order, so for instance to take the greatest element is an O(1) operation. Insertion and deletion is O(log(N)). Sorted sets are implemented using a dual ported data structure consisting of an hash table and a skip list. For more information please read the <a href="IntroductionToRedisDataTypes.html">Introduction To Redis Data Types</a>.<h2><a name="Specialized integer objects encoding">Specialized integer objects encoding</a></h2>Redis 1.2 will use less memory than Redis 1.0 for values in Strings, Lists or Sets elements that happen to be representable as 32 or 64 bit signed integers (it depends on your arch bits for the long C type). This is totally transparent form the point of view of the user, but will safe a lot of memory (30% less in datasets where there are many integers).<h2><a name="MSET and MSETNX">MSET and MSETNX</a></h2>That is, setting multiple keys in one command, atomically. For more information see the <a href="MsetCommand.html">MSET command</a> wiki page.<h2><a name="Better Performances">Better Performances</a></h2><ul><li> 100x times faster SAVE and BGSAVE! There was a problem in the LZF lib configuration that is now resolved. The effect is this impressive speedup. Also the saving child will no longer use 100% of CPU.</li><li> Glue output buffer and writev(). Many commands producing large outputs, like LRANGE, will now be even 10 times faster, thanks to the new output buffer gluing algorithm and the (optional) use of writev(2) syscall.</li><li> Support for epool and kqueue / kevent. 10,000 clients scalability.</li><li> Much better EXPIRE support, now it's possible to work with very large sets of keys expiring in very short time without to incur in memory problems (the new algorithm expires keys in an adaptive way, so will get more aggressive if there are a lot of expiring keys)</li></ul>
<h2><a name="Solaris Support">Solaris Support</a></h2>Redis will now compile and work on Solaris without problems. Warning: the Solaris user base is very little, so Redis running on Solaris may not be as tested and stable as it is on Linux and Mac OS X.<h2><a name="Support for the new generation protocol">Support for the new generation protocol</a></h2><ul><li> Redis is now able to accept commands in a new fully binary safe way: with the new protocol keys are binary safe, not only values, and there is no distinction between bulk commands and inline commands. This new protocol is currently used only for MSET and MSETNX but at some point it will hopefully replace the old one. See the Multi Bulk Commands section in the <a href="ProtocolSpecification.html">Redis Protocol Specification</a> for more information.</li></ul>
<h2><a name="A few new commands about already supported data types">A few new commands about already supported data types</a></h2><ul><li> <a href="SrandmemberCommand.html">SRANDMEMBER</a></li><li> The <a href="SortCommand.html">SortCommand</a> is now supprots the <b>STORE</b> and <b>GET #</b> forms, the first can be used to save sorted lists, sets or sorted sets into keys for caching. Check the manual page for more information about the <b>GET #</b> form.</li><li> The new <a href="RpoplpushCommand.html">RPOPLPUSH command</a> can do many interesting magics, and a few of this are documented in the wiki page of the command.</li></ul>
<h2><a name="Bug fixing">Bug fixing</a></h2>Of course, many bugs are now fixed, and I bet, a few others introduced: this is how software works after all, so make sure to report issues in the Redis mailing list or in the Google Code issues tracker.<br/><br/>Enjoy!
antirez<h1><a name="CHANGELOG for Redis 1.1.90">CHANGELOG for Redis 1.1.90</a></h1><ul><li> 2009-09-10 in-memory specialized object encoding. (antirez)</li><li> 2009-09-17 maxmemory fixed in 64 systems for values &gt; 4GB. (antirez)</li><li> 2009-10-07 multi-bulk protocol implemented. (antriez)</li><li> 2009-10-16 MSET and MSETNX commands implemented (antirez)</li><li> 2009-10-21 SRANDMEMBER added (antirez)</li><li> 2009-10-23 Fixed compilation in mac os x snow leopard when compiling a 32 bit binary. (antirez)</li><li> 2009-10-23 New data type: Sorted sets and Z-commands (antirez)</li><li> 2009-10-26 Solaris fixed (Alan Harder)</li><li> 2009-10-29 Fixed Issue a number of open issues (antirez)</li><li> 2009-10-30 New persistence mode: append only file (antirez)</li><li> 2009-11-01 SORT STORE option (antirez)</li><li> 2009-11-03 redis-cli now accepts a -r (repeat) switch. (antirez)</li><li> 2009-11-04 masterauth option merged (Anthony Lauzon)</li><li> 2009-11-04 redis-test is now a better Redis citizen, testing everything against DB 9 and 10 and only if this DBs are empty. (antirez)</li><li> 2009-11-10 Implemented a much better lazy expiring algorithm for EXPIRE (antirez)</li><li> 2009-11-11 RPUSHLPOP (antirez from an idea of @ezmobius)</li><li> 2009-11-12 Merge git://github.com/ianxm/redis (Can't remmber what this implements, sorry)</li><li> 2009-11-17 multi-bulk reply support for redis-bench, LRANGE speed tests (antirez)</li><li> 2009-11-17 support for writev implemented. (Stefano Barbato)</li><li> 2009-11-19 debug mode (-D) in redis-bench (antirez)</li><li> 2009-11-21 SORT GET # implemented (antirez)</li><li> 2009-11-23 ae.c made modular, with support for epoll. (antirez)</li><li> 2009-11-26 background append log rebuilding (antirez)</li><li> 2009-11-28 Added support for kqueue. (Harish Mallipeddi)</li><li> 2009-11-29 SORT support for sorted sets (antirez, thanks to @tobi for the idea)</li></ul>
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<b>Redis_2_0_0_Changelog: Contents</b><br>&nbsp;&nbsp;<a href="#Redis 2.0: What's new?">Redis 2.0: What's new?</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#MULTI/EXEC">MULTI/EXEC</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Blocking pop">Blocking pop</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Publish/subscribe">Publish/subscribe</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Hashes">Hashes</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Virtual Memory">Virtual Memory</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Contributors">Contributors</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Special Thanks">Special Thanks</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#DOWNLOAD">DOWNLOAD</a>
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<h1><a name="Redis 2.0: What's new?">Redis 2.0: What's new?</a></h1>The release of Redis 2.0 marks a major milestone in Redis development. Apart from an endless list of new features, there are some major ones that deserve to be highlighted.<br/><br/>It's worth to mention that while Redis 2.0.0 just reached its first stable release, Redis 2.2.0 is near to reach feature freeze, so ... be prepared for new exiting things in very short time!<h3><a name="MULTI/EXEC">MULTI/EXEC</a></h3>
The MULTI/EXEC family of commands were added to fulfill the need to execute multiple commands as a single atomic block.
Because all commands inside a MULTI/EXEC block are serialized and executed sequentially, it is not possible that another
client request is served in the middle of executing this block. All commands are executed one after the other when
EXEC is called, which makes sure either <b>all</b> or <b>no</b> commands are executed, independent of the state of the client connection.<br/><br/>More on MULTI/EXEC:
<ul><li> <a href="http://code.google.com/p/redis/wiki/MultiExecCommand" target="_blank">http://code.google.com/p/redis/wiki/MultiExecCommand</a></li></ul>
Note that WATCH, a CAS (check and set) variant of MULTI/EXEC will be available on 2.2.0 and is not part of 2.0.0.<h3><a name="Blocking pop">Blocking pop</a></h3>
The commands BLPOP and BRPOP were added to support popping from a list in a blocking fashion. This means the client
connection will be blocked for a certain amount of time until another client pushes an item on a list. These commands
are frequently used in producer/consumer scenarios.<br/><br/>More on blocking pop:
<ul><li> <a href="http://code.google.com/p/redis/wiki/BlpopCommand" target="_blank">http://code.google.com/p/redis/wiki/BlpopCommand</a></li></ul>
<h3><a name="Publish/subscribe">Publish/subscribe</a></h3>
The family of publish/subscribe commands let clients publish messages onto channels and subscribe to receive all messages
that are published on channels. Also included are commands to receive all messages for which the channel matches a given pattern.<br/><br/>More on publish/subscribe:
<ul><li> <a href="http://code.google.com/p/redis/wiki/PublishSubscribe" target="_blank">http://code.google.com/p/redis/wiki/PublishSubscribe</a></li><li> <a href="http://antirez.com/post/redis-weekly-update-3-publish-submit.html" target="_blank">http://antirez.com/post/redis-weekly-update-3-publish-submit.html</a></li><li> <a href="http://rediscookbook.org/pubsub_for_asynchronous_communication.html" target="_blank">http://rediscookbook.org/pubsub_for_asynchronous_communication.html</a></li></ul>
<h3><a name="Hashes">Hashes</a></h3>
This new datatype allows to store multiple key/value pairs on a single key. Together with the list of regular commands you
would expect for such a datatype (HSET, HGET, HDEL, HLEN, HKEYS, ...), it is also possible to use the values <i>inside</i> a hash
for any SORT operation.<br/><br/>More on hashes:
<ul><li> <a href="http://code.google.com/p/redis/wiki/HsetCommand" target="_blank">http://code.google.com/p/redis/wiki/HsetCommand</a></li><li> <a href="http://antirez.com/post/redis-weekly-update-1.html" target="_blank">http://antirez.com/post/redis-weekly-update-1.html</a></li></ul>
<h3><a name="Virtual Memory">Virtual Memory</a></h3>
Redis Virtual Memory allows users to grow their dataset beyond the limits of their RAM.<br/><br/>More on virtual memory:
<ul><li> <a href="http://code.google.com/p/redis/wiki/VirtualMemoryUserGuide" target="_blank">http://code.google.com/p/redis/wiki/VirtualMemoryUserGuide</a></li><li> <a href="http://antirez.com/post/redis-virtual-memory-story.html" target="_blank">http://antirez.com/post/redis-virtual-memory-story.html</a></li></ul>
<h3><a name="Contributors">Contributors</a></h3><ul><li> Salvatore Sanfilippo</li><li> Pieter Noordhuis</li><li> Antonio Ognio</li><li> Alex McHale</li><li> Michel Martens</li><li> Damian Janowski</li><li> Bruno Deferrari</li><li> Ashley Martens</li><li> Derek Collison</li><li> Damian Janowski</li><li> Jeremy Zawodny</li><li> Konstantin Merenkov</li><li> Michel Martens</li><li> Sam Hendley</li></ul>
<h3><a name="Special Thanks">Special Thanks</a></h3>
Thanks to VMware sponsoring the work of Salvatore and Pieter, and the Redis community of users and client library developers. Redis 2.0.0 was possible only thanks to your support.<h3><a name="DOWNLOAD">DOWNLOAD</a></h3>
You can grab Redis 2.0.0 from <a href="http://code.google.com/p/redis/downloads/list" target="_blank">Google Code</a>.<br/><br/>It is also tagged on Git.
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<b>Redis_2_0_Whats_new: Contents</b><br>&nbsp;&nbsp;<a href="#Redis 2.0: What's new?">Redis 2.0: What's new?</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#MULTI/EXEC">MULTI/EXEC</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Blocking pop">Blocking pop</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Publish/subscribe">Publish/subscribe</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Hashes">Hashes</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Virtual Memory">Virtual Memory</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Contributors">Contributors</a>
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<h1 class="wikiname">Redis_2_0_Whats_new</h1>
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<h1><a name="Redis 2.0: What's new?">Redis 2.0: What's new?</a></h1>The release of Redis 2.0 marks a major milestone in Redis development. Apart from an endless list of new features, there are some major ones that deserve to be highlighted.<h3><a name="MULTI/EXEC">MULTI/EXEC</a></h3>
The MULTI/EXEC family of commands were added to fulfill the need to execute multiple commands as a single atomic block.
Because all commands inside a MULTI/EXEC block are serialized and executed sequentially, it is not possible that another
client request is served in the middle of executing this block. All commands are executed one after the other when
EXEC is called, which makes sure either <b>all</b> or <b>no</b> commands are executed, independent of the state of the client connection.<br/><br/>More on MULTI/EXEC:
<ul><li> <a href="http://code.google.com/p/redis/wiki/MultiExecCommand" target="_blank">http://code.google.com/p/redis/wiki/MultiExecCommand</a></li></ul>
<h3><a name="Blocking pop">Blocking pop</a></h3>
The commands BLPOP and BRPOP were added to support popping from a list in a blocking fashion. This means the client
connection will be blocked for a certain amount of time until another client pushes an item on a list. These commands
are frequently used in producer/consumer scenarios.<br/><br/>More on blocking pop:
<ul><li> <a href="http://code.google.com/p/redis/wiki/BlpopCommand" target="_blank">http://code.google.com/p/redis/wiki/BlpopCommand</a></li></ul>
<h3><a name="Publish/subscribe">Publish/subscribe</a></h3>
The family of publish/subscribe commands let clients publish messages onto channels and subscribe to receive all messages
that are published on channels. Also included are commands to receive all messages for which the channel matches a given pattern.<br/><br/>More on publish/subscribe:
<ul><li> <a href="http://code.google.com/p/redis/wiki/PublishSubscribe" target="_blank">http://code.google.com/p/redis/wiki/PublishSubscribe</a></li><li> <a href="http://antirez.com/post/redis-weekly-update-3-publish-submit.html" target="_blank">http://antirez.com/post/redis-weekly-update-3-publish-submit.html</a></li><li> <a href="http://rediscookbook.org/pubsub_for_asynchronous_communication.html" target="_blank">http://rediscookbook.org/pubsub_for_asynchronous_communication.html</a></li></ul>
<h3><a name="Hashes">Hashes</a></h3>
This new datatype allows to store multiple key/value pairs on a single key. Together with the list of regular commands you
would expect for such a datatype (HSET, HGET, HDEL, HLEN, HKEYS, ...), it is also possible to use the values <i>inside</i> a hash
for any SORT operation.<br/><br/>More on hashes:
<ul><li> <a href="http://code.google.com/p/redis/wiki/HsetCommand" target="_blank">http://code.google.com/p/redis/wiki/HsetCommand</a></li><li> <a href="http://antirez.com/post/redis-weekly-update-1.html" target="_blank">http://antirez.com/post/redis-weekly-update-1.html</a></li></ul>
<h3><a name="Virtual Memory">Virtual Memory</a></h3>
Redis Virtual Memory allows users to grow their dataset beyond the limits of their RAM.<br/><br/>More on virtual memory:
<ul><li> <a href="http://code.google.com/p/redis/wiki/VirtualMemoryUserGuide" target="_blank">http://code.google.com/p/redis/wiki/VirtualMemoryUserGuide</a></li><li> <a href="http://antirez.com/post/redis-virtual-memory-story.html" target="_blank">http://antirez.com/post/redis-virtual-memory-story.html</a></li></ul>
<h2><a name="Contributors">Contributors</a></h2><ul><li> Salvatore Sanfilippo</li><li> Pieter Noordhuis</li><li> Antonio Ognio</li><li> Alex McHale</li><li> Michel Martens</li><li> Damian Janowski</li><li> Bruno Deferrari</li><li> Ashley Martens</li><li> Derek Collison</li><li> Damian Janowski</li><li> Jeremy Zawodny</li><li> Konstantin Merenkov</li><li> Michel Martens</li><li> Sam Hendley</li></ul>
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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>
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&iuml;&raquo;&iquest;#sidebar <a href="GenericCommandsSidebar.html">GenericCommandsSidebar</a><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>
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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>
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<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
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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 slave 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, to the slave, as a stream of commands, in the same format of the Redis protocol itself.<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="#Features added in past versions">Features added in past versions</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#1.1 / 1.2">1.1 / 1.2</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#0.x / 1.0">0.x / 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="Features added in past versions">Features added in past versions</a></h2><h2><a name="1.1 / 1.2">1.1 / 1.2</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="0.x / 1.0">0.x / 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>
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&iuml;&raquo;&iquest;#sidebar <a href="ListCommandsSidebar.html">ListCommandsSidebar</a><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>
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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>
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&iuml;&raquo;&iquest;#sidebar <a href="ListCommandsSidebar.html">ListCommandsSidebar</a><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 (LPUSH) or tail (RPUSH) 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">Integer reply</a>, specifically, the number of elements inside the list after the push operation.
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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>
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<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 iscreated. 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
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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>
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<blockquote>Save the whole dataset on disk (this means that all the databases are saved, as well as keys with an EXPIRE set (the expire is preserved). 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>
<blockquote>The background variant of this command is <a href="BgsaveCommand.html">BGSAVE</a> that is able to perform the saving in the background while the server continues serving other clients.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a>
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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>
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<h1 class="wikiname">ScardCommand</h1>
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&iuml;&raquo;&iquest;#sidebar <a href="SetCommandsSidebar.html">SetCommandsSidebar</a><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.
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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>
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<h1 class="wikiname">SdiffCommand</h1>
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&iuml;&raquo;&iquest;#sidebar <a href="SetCommandsSidebar.html">SetCommandsSidebar</a><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.
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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>
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<h1 class="wikiname">SdiffstoreCommand</h1>
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&iuml;&raquo;&iquest;#sidebar <a href="SetCommandsSidebar.html">SetCommandsSidebar</a><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 command works exactly like SDIFF but instead of being returned the resulting set is stored in <i>dstkey</i>.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a>
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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>
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<h1 class="wikiname">SelectCommand</h1>
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&iuml;&raquo;&iquest;#sidebar <a href="GenericCommandsSidebar.html">GenericCommandsSidebar</a><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>
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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>
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<h1 class="wikiname">SetCommand</h1>
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&iuml;&raquo;&iquest;#sidebar <a href="StringCommandsSidebar.html">StringCommandsSidebar</a><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>
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<b>SetCommandsSidebar: Contents</b>
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&iuml;&raquo;&iquest;== Set Commands ==<br/><br/><ul><li> <a href="SaddCommand.html">SADD</a></li><li> <a href="SremCommand.html">SREM</a></li><li> <a href="SpopCommand.html">SPOP</a></li><li> <a href="SmoveCommand.html">SMOVE</a></li><li> <a href="ScardCommand.html">SCARD</a></li><li> <a href="SismemberCommand.html">SISMEMBER</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="SunionstoreCommand.html">SUNIONSTORE</a></li><li> <a href="SdiffCommand.html">SDIFF</a></li><li> <a href="SdiffstoreCommand.html">SDIFFSTORE</a></li><li> <a href="SmembersCommand.html">SMEMBERS</a></li><li> <a href="SrandmemberCommand.html">SRANDMEMBER</a></li><li> <a href="SortCommand.html">SORT</a></li></ul>
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