[redis.git] / doc / SetrangeCommand.html


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<!-- This is a (PRE) block.  Make sure it's left aligned or your toc title will be off. -->
<b>SetrangeCommand: Contents</b><br>&nbsp;&nbsp;<a href="#SETRANGE _key_ _offset_ _value_ (Redis &gt;">SETRANGE _key_ _offset_ _value_ (Redis &gt;</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Examples">Examples</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Patterns">Patterns</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
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                <h1 class="wikiname">SetrangeCommand</h1>

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                    &iuml;&raquo;&iquest;#sidebar <a href="StringCommandsSidebar.html">StringCommandsSidebar</a><h1><a name="SETRANGE _key_ _offset_ _value_ (Redis &gt;">SETRANGE _key_ _offset_ _value_ (Redis &gt;</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&gt; set foo &quot;Hello World&quot;
OK
redis&gt; setrange foo 6 &quot;Redis&quot;
(integer) 11
redis&gt; get foo
&quot;Hello Redis&quot;
</pre>Example of the zero padding behavior.<br/><br/><pre class="codeblock python python" name="code">
redis&gt; del foo
(integer) 1
redis&gt; setrange foo 10 bar
(integer) 13
redis&gt; get foo
&quot;\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bar&quot;
</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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	18	<!-- This is a (PRE) block. Make sure it's left aligned or your toc title will be off. -->
	19	<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>
	20	</div>
	21
	22	<h1 class="wikiname">SetrangeCommand</h1>
	23
	24	<div class="summary">
	25
	26	</div>
	27
	28	<div class="narrow">
	29	ï»¿#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) =
	30	<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>
	31	<h2><a name="Examples">Examples</a></h2>First example, basic usage setting a range.<br/><br/><pre class="codeblock python" name="code">
	32	redis> set foo "Hello World"
	33	OK
	34	redis> setrange foo 6 "Redis"
	35	(integer) 11
	36	redis> get foo
	37	"Hello Redis"
	38	</pre>Example of the zero padding behavior.<br/><br/><pre class="codeblock python python" name="code">
	39	redis> del foo
	40	(integer) 1
	41	redis> setrange foo 10 bar
	42	(integer) 13
	43	redis> get foo
	44	"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bar"
	45	</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.
	46	On a 2010 Macbook Pro, setting byte number 536870911 (512MB allocation) takes ~300ms,
	47	setting byte number 134217728 (128MB allocation) takes ~80ms,
	48	setting bit number 33554432 (32MB allocation) takes ~30ms and
	49	setting bit number 8388608 (8MB allocation) takes ~8ms.
	50	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.
	51
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	57	</html>
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