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SetrangeCommand.html
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SetrangeCommand.html
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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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<h1 class="wikiname">SetrangeCommand</h1>
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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) =
<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>
<h2><a name="Examples">Examples</a></h2>First example, basic usage setting a range.<br/><br/><pre class="codeblock python" name="code">
redis> set foo "Hello World"
OK
redis> setrange foo 6 "Redis"
(integer) 11
redis> get foo
"Hello Redis"
</pre>Example of the zero padding behavior.<br/><br/><pre class="codeblock python python" name="code">
redis> del foo
(integer) 1
redis> setrange foo 10 bar
(integer) 13
redis> get foo
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bar"
</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.
On a 2010 Macbook Pro, setting byte number 536870911 (512MB allocation) takes ~300ms,
setting byte number 134217728 (128MB allocation) takes ~80ms,
setting bit number 33554432 (32MB allocation) takes ~30ms and
setting bit number 8388608 (8MB allocation) takes ~8ms.
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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