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Lists.html
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Lists.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
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<link type="text/css" rel="stylesheet" href="style.css" />
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<div id="page">
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<a href="index.html">
<img style="border:none" alt="Redis Documentation" src="redis.png">
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<div id="pagecontent">
<div class="index">
<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
<b>Lists: Contents</b><br> <a href="#Redis List Type">Redis List Type</a><br> <a href="#Implementation details">Implementation details</a>
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<h1 class="wikiname">Lists</h1>
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#sidebar <a href="ListCommandsSidebar.html">ListCommandsSidebar</a><h1><a name="Redis List Type">Redis List Type</a></h1>Redis Lists are lists of <a href="Strings.html">Redis Strings</a>, sorted by insertion order. It's possible to add elements to a Redis List pushing new elements on the head (on the left) or on the tail (on the right) of the list.<br/><br/>The <a href="RpushCommand.html">LPUSH</a> command inserts a new elmenet on head, while <a href="RpushCommand.html">RPUSH</a> inserts a new element on tail. A new list is created when one of this operations is performed against an empty key.<br/><br/>For instance if perform the following operations:
<pre class="codeblock python" name="code">
LPUSH mylist a # now the list is "a"
LPUSH mylist b # now the list is "b","a"
RPUSH mylist c # now the list is "b","a","c" (RPUSH was used this time)
</pre>
The resulting list stored at <i>mylist</i> will contain the elements "b","a","c".<br/><br/>The max length of a list is 232-1 elements (4294967295, more than 4 billion of elements per list).<h1><a name="Implementation details">Implementation details</a></h1>Redis Lists are implemented as doubly liked lists. A few commands benefit from the fact the lists are doubly linked in order to reach the needed element starting from the nearest extreme (head or tail). <a href="LrangeCommand.html">LRANGE</a> and <a href="LindexCommand.html">LINDEX</a> are examples of such commands.<br/><br/>The use of linked lists also guarantees that regardless of the length of the list pushing and popping are O(1) operations.<br/><br/>Redis Lists cache length information so <a href="LlenCommand.html">LLEN</a> is O(1) as well.
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