searchcode | source code search engine

19 <b>TwitterAlikeExample: Contents</b><br>  <a href="#A case study: Design and implementation of a simple Twitter clone using only the Redis key-value store as database and PHP">A case study: Design and implementation of a simple Twitter clone using only the Redis key-value store as database and PHP</a><br>  <a href="#Key-value stores basics">Key-value stores basics</a><br>    <a href="#Atomic operations">Atomic operations</a><br>    <a href="#Beyond key-value stores">Beyond key-value stores</a><br>      <a href="#The set data type">The set data type</a><br>    <a href="#Prerequisites">Prerequisites</a><br>    <a href="#Data layout">Data layout</a><br>    <a href="#Following, followers and updates">Following, followers and updates</a><br>    <a href="#Authentication">Authentication</a><br>    <a href="#Updates">Updates</a><br>    <a href="#Paginating updates">Paginating updates</a><br>    <a href="#Following users">Following users</a><br>  <a href="#Making it horizontally scalable">Making it horizontally scalable</a><br>      <a href="#Hashing the key">Hashing the key</a><br>      <a href="#Special keys">Special keys</a>

20 </div>

21

27

28 <div class="narrow">

29 <h1><a name="A case study: Design and implementation of a simple Twitter clone using only the Redis key-value store as database and PHP">A case study: Design and implementation of a simple Twitter clone using only the Redis key-value store as database and PHP</a></h1>In this article I'll explain the design and the implementation of a <a href="http://retwis.antirez.com" target="_blank">simple clone of Twitter</a> written using PHP and <a href="http://code.google.com/p/redis/" target="_blank">Redis</a> as only database. The programming community uses to look at key-value stores like special databases that can't be used as drop in replacement for a relational database for the development of web applications. This article will try to prove the contrary.<br/><br/>Our Twitter clone, <a href="http://retwis.antirez.com" target="_blank">called Retwis</a>, is structurally simple, has very good performances, and can be distributed among N web servers and M Redis servers with very little efforts. You can find the source code <a href="http://code.google.com/p/redis/downloads/list" target="_blank">here</a>.<br/><br/>We use PHP for the example since it can be read by everybody. The same (or... much better) results can be obtained using Ruby, Python, Erlang, and so on.

30 <h1><a name="Key-value stores basics">Key-value stores basics</a></h1>

31 The essence of a key-value store is the ability to store some data, called <i>value</i>, inside a key. This data can later be retrieved only if we know the exact key used to store it. There is no way to search something by value. So for example I can use the command SET to store the value <b>bar</b> at key <b>foo</b>:<br/><br/><pre class="codeblock python" name="code">

79 </pre>Ok I think we are ready to start coding!

80 <h2><a name="Prerequisites">Prerequisites</a></h2>

81 If you didn't download it already please <a href="http://code.google.com/p/redis/wiki/README" target="_blank">grab the source code of Retwis</a>. It's a simple tar.gz file with a few of .php files inside. The implementation is very simple. You will find the PHP library client inside (redis.php) that is used to talk with the Redis server from PHP. This library was written by <a href="http://qix.it" target="_blank">Ludovico Magnocavallo</a> and you are free to reuse this in your own projects, but for updated version of the library please download the Redis distribution.<br/><br/>Another thing you probably want is a working Redis server. Just get the source, compile with make, and run with ./redis-server and you are done. No configuration is required at all in order to play with it or to run Retwis in your computer.

82 <h2><a name="Data layout">Data layout</a></h2>

83 Working with a relational database this is the stage were the database layout should be produced in form of tables, indexes, and so on. We don't have tables, so what should be designed? We need to identify what keys are needed to represent our objects and what kind of values this keys need to hold.<br/><br/>Let's start from Users. We need to represent this users of course, with the username, userid, password, followers and following users, and so on. The first question is, what should identify an user inside our system? The username can be a good idea since it is unique, but it is also too big, and we want to stay low on memory. So like if our DB was a relational one we can associate an unique ID to every user. Every other reference to this user will be done by id. That's very simple to do, because we have our atomic INCR operation! When we create a new user we can do something like this, assuming the user is callled "antirez":<br/><br/><pre class="codeblock python python python python python python python python python python python python" name="code">