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http://github.com/valkey-io/valkey
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59 lines
3.6 KiB
HTML
59 lines
3.6 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<html>
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<head>
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<link type="text/css" rel="stylesheet" href="style.css" />
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</head>
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<body>
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<div id="page">
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<div id='header'>
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<a href="index.html">
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<img style="border:none" alt="Redis Documentation" src="redis.png">
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</a>
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</div>
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<div id="pagecontent">
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<div class="index">
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<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
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<b>SetrangeCommand: Contents</b><br> <a href="#SETRANGE _key_ _offset_ _value_ (Redis >">SETRANGE _key_ _offset_ _value_ (Redis ></a><br> <a href="#Examples">Examples</a><br> <a href="#Patterns">Patterns</a><br> <a href="#Return value">Return value</a>
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</div>
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<h1 class="wikiname">SetrangeCommand</h1>
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<div class="summary">
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</div>
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<div class="narrow">
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#sidebar <a href="StringCommandsSidebar.html">StringCommandsSidebar</a><h1><a name="SETRANGE _key_ _offset_ _value_ (Redis >">SETRANGE _key_ _offset_ _value_ (Redis ></a></h1> 2.1.8) =
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<i>Time complexity: O(1) not counting the time taken to copy the new string in place, as usually this string is small so the amoritzed time is O(1). Otheriwse O(M) with M being the length of the value argument</i><blockquote>Overwrites part of a string at <i>key</i> starting at the specified offset,for all the length of <i>value</i>.If the offset is over the old length of the string, the string is paddedwith zero bytes until needed. Non existing keys are considered likealready containing an empty string.</blockquote>
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<h2><a name="Examples">Examples</a></h2>First example, basic usage setting a range.<br/><br/><pre class="codeblock python" name="code">
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redis> set foo "Hello World"
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OK
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redis> setrange foo 6 "Redis"
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(integer) 11
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redis> get foo
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"Hello Redis"
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</pre>Example of the zero padding behavior.<br/><br/><pre class="codeblock python python" name="code">
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redis> del foo
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(integer) 1
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redis> setrange foo 10 bar
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(integer) 13
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redis> get foo
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"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bar"
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</pre>Note that the maximum offset that you can set is 536870911 as Redis Strings are limited to 512 megabytes. You can still create longer arrays of values using multiple keys.<br/><br/><b>Warning</b>: When setting the last possible byte and the string value stored at <i>key</i> does not yet hold a string value, or holds a small string value, Redis needs to allocate all intermediate memory which can block the server for some time.
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On a 2010 Macbook Pro, setting byte number 536870911 (512MB allocation) takes ~300ms,
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setting byte number 134217728 (128MB allocation) takes ~80ms,
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setting bit number 33554432 (32MB allocation) takes ~30ms and
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setting bit number 8388608 (8MB allocation) takes ~8ms.
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Note that once this first allocation is done, subsequent calls to SETRANGE for the same <i>key</i> will not have the allocation overhead.<h2><a name="Patterns">Patterns</a></h2>Thanks to SETRANGE and the analogous GETRANGE command you can use Redis strings as a linear array of memory with O(1) random access. This is a very fast and efficient storage in many real world use cases.<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically: the length of the string after it was modified by the command.
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</div>
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</div>
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</div>
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</body>
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</html>
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