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<b>FlushdbCommand: Contents</b><br>&nbsp;&nbsp;<a href="#FLUSHDB">FLUSHDB</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">FlushdbCommand</h1>
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<h1><a name="FLUSHDB">FLUSHDB</a></h1>
<blockquote>Delete all the keys of the currently selected DB. This command never fails.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="FlushallCommand.html">FLUSHALL</a></li></ul>
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<b>GetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#GET _key_">GET _key_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">GetCommand</h1>
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<h1><a name="GET _key_">GET _key_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Get the value of the specified key. If the keydoes not exist the special value 'nil' is returned.If the value stored at <i>key</i> is not a string an erroris returned because GET can only handle string values.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="SetCommand.html">SET</a></li><li> <a href="SetnxCommand.html">SETNX</a></li><li> <a href="IncrCommand.html">INCR</a></li></ul>
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<b>IncrCommand: Contents</b><br>&nbsp;&nbsp;<a href="#INCR _key_">INCR _key_</a><br>&nbsp;&nbsp;<a href="#INCRBY _key_ _integer_">INCRBY _key_ _integer_</a><br>&nbsp;&nbsp;<a href="#DECR _key_ _integer_">DECR _key_ _integer_</a><br>&nbsp;&nbsp;<a href="#DECRBY _key_ _integer_">DECRBY _key_ _integer_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">IncrCommand</h1>
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<h1><a name="INCR _key_">INCR _key_</a></h1>
<h1><a name="INCRBY _key_ _integer_">INCRBY _key_ _integer_</a></h1>
<h1><a name="DECR _key_ _integer_">DECR _key_ _integer_</a></h1>
<h1><a name="DECRBY _key_ _integer_">DECRBY _key_ _integer_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Increment or decrement the number stored at <i>key</i> by one. If the key doesnot exist or contains a value of a wrong type, set the key to thevalue of &quot;0&quot; before to perform the increment or decrement operation.</blockquote>
<blockquote>INCRBY and DECRBY work just like INCR and DECR but instead toincrement/decrement by 1 the increment/decrement is <i>integer</i>.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, this commands will reply with the new value of <i>key</i> after the increment or decrement.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="GetCommand.html">GET</a></li></ul>
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<b>InfoCommand: Contents</b><br>&nbsp;&nbsp;<a href="#INFO">INFO</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Notes">Notes</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">InfoCommand</h1>
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<h1><a name="INFO">INFO</a></h1><blockquote>The info command returns different information and statistics about the server in an format that's simple to parse by computers and easy to red by huamns.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a>, specifically in the following format:<br/><br/><pre class="codeblock python" name="code">
edis_version:0.07
connected_clients:1
connected_slaves:0
used_memory:3187
changes_since_last_save:0
last_save_time:1237655729
total_connections_received:1
total_commands_processed:1
uptime_in_seconds:25
uptime_in_days:0
</pre>All the fields are in the form <code name="code" class="python">field:value</code><h2><a name="Notes">Notes</a></h2><ul><li> <code name="code" class="python">used_memory</code> is returned in bytes, and is the total number of bytes allocated by the program using <code name="code" class="python">malloc</code>.</li><li> <code name="code" class="python">uptime_in_days</code> is redundant since the uptime in seconds contains already the full uptime information, this field is only mainly present for humans.</li><li> <code name="code" class="python">changes_since_last_save</code> does not refer to the number of key changes, but to the number of operations that produced some kind of change in the dataset.</li></ul>
<h2><a name="See also">See also</a></h2>
<ul><li> <a href="LastsaveCommand.html">LASTSAVE</a></li><li> <a href="DbsizeCommand.html">DBSIZE</a></li></ul>
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<b>KeysCommand: Contents</b><br>&nbsp;&nbsp;<a href="#KEYS _pattern_">KEYS _pattern_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">KeysCommand</h1>
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<h1><a name="KEYS _pattern_">KEYS _pattern_</a></h1>
<i>Time complexity: O(n) (with n being the number of keys in the DB, and assuming keys and pattern of limited length)</i><blockquote>Returns all the keys matching the glob-style <i>pattern</i> asspace separated strings. For example if you have in thedatabase the keys &quot;foo&quot; and &quot;foobar&quot; the command &quot;KEYS foo<code name="code" class="python">*</code>&quot;will return &quot;foo foobar&quot;.</blockquote>
<blockquote>Note that while the time complexity for this operation is O(n)the constant times are pretty low. For example Redis runningon an entry level laptop can scan a 1 million keys databasein 40 milliseconds. Still it's better to consider this one ofthe slow commands that may ruin the DB performance if not usedwith care.</blockquote>
Glob style patterns examples:
<ul><li> h?llo will match hello hallo hhllo</li><li> h<b>llo will match hllo heeeello
<blockquote>* h<a href="ae.html">ae</a>llo will match hello and hallo, but not hillo</blockquote>Use \ to escape special chars if you want to match them verbatim.<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a>, specifically a string in the form of space separated list of keys. Note that most client libraries will return an Array of keys and not a single string with space separated keys (that is, split by &quot; &quot; is performed in the client library usually).<h2><a name="See also">See also</a></h2>
<blockquote>* <a href="RandomkeyCommand.html">RANDOMKEY</a> to get the name of a randomly selected key in O(1).</blockquote></b></li></ul>
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<b>LastsaveCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LASTSAVE">LASTSAVE</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LastsaveCommand</h1>
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<h1><a name="LASTSAVE">LASTSAVE</a></h1>
<blockquote>Return the UNIX TIME of the last DB save executed with success.A client may check if a <a href="BgsaveCommand.html">BGSAVE</a> command succeeded reading the LASTSAVEvalue, then issuing a <a href="BgsaveCommand.html">BGSAVE</a> command and checking at regular intervalsevery N seconds if LASTSAVE changed.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically an UNIX time stamp.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="BgsaveCommand.html">BGSAVE</a></li></ul>
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<b>LindexCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LINDEX _key_ _index_">LINDEX _key_ _index_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LindexCommand</h1>
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<h1><a name="LINDEX _key_ _index_">LINDEX _key_ _index_</a></h1>
<i>Time complexity: O(n) (with n being the length of the list)</i><blockquote>Return the specified element of the list stored at the specifiedkey. 0 is the first element, 1 the second and so on. Negative indexesare supported, for example -1 is the last element, -2 the penultimateand so on.</blockquote>
<blockquote>If the value stored at key is not of list type an error is returned.If the index is out of range an empty string is returned.</blockquote>
<blockquote>Note that even if the average time complexity is O(n) asking forthe first or the last element of the list is O(1).</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a>, specifically the requested element.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LlenCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LLEN _key_">LLEN _key_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LlenCommand</h1>
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<h1><a name="LLEN _key_">LLEN _key_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Return the length of the list stored at the specified key. If thekey does not exist zero is returned (the same behaviour as forempty lists). If the value stored at <i>key</i> is not a list an error is returned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
The length of the list as an integer `&gt;=` 0 if the operation succeeded
-2 if the specified key does not hold a list value
</pre>Note that library clients should raise an error if -2 is returned by the Redis server instead to pass the negative value back to the caller.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LpopCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LPOP _key_">LPOP _key_</a><br>&nbsp;&nbsp;<a href="#RPOP _key_">RPOP _key_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LpopCommand</h1>
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<h1><a name="LPOP _key_">LPOP _key_</a></h1>
<h1><a name="RPOP _key_">RPOP _key_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Atomically return and remove the first (LPOP) or last (RPOP) elementof the list. For example if the list contains the elements &quot;a&quot;,&quot;b&quot;,&quot;c&quot; LPOPwill return &quot;a&quot; and the list will become &quot;b&quot;,&quot;c&quot;.</blockquote>
<blockquote>If the <i>key</i> does not exist or the list is already empty the specialvalue 'nil' is returned.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Bulk reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LrangeCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LRANGE _key_ _start_ _end_">LRANGE _key_ _start_ _end_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LrangeCommand</h1>
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<h1><a name="LRANGE _key_ _start_ _end_">LRANGE _key_ _start_ _end_</a></h1>
<i>Time complexity: O(n) (with n being the length of the range)</i><blockquote>Return the specified elements of the list stored at the specifiedkey. Start and end are zero-based indexes. 0 is the first elementof the list (the list head), 1 the next element and so on.</blockquote>
<blockquote>For example LRANGE foobar 0 2 will return the first three elementsof the list.</blockquote>
<blockquote>_start_ and <i>end</i> can also be negative numbers indicating offsetsfrom the end of the list. For example -1 is the last element ofthe list, -2 the penultimate element and so on.</blockquote>
<blockquote>Indexes out of range will not produce an error: if start is overthe end of the list, or start <code name="code" class="python">&gt;</code> end, an empty list is returned.If end is over the end of the list Redis will threat it just likethe last element of the list.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Multi bulk reply</a>, specifically a list of elements in the specified range.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LremCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LREM _key_ _count_ _value_">LREM _key_ _count_ _value_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LremCommand</h1>
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<h1><a name="LREM _key_ _count_ _value_">LREM _key_ _count_ _value_</a></h1>
<i>Time complexity: O(N) (with N being the length of the list)</i><blockquote>Remove the first <i>count</i> occurrences of the <i>value</i> element from the list.If <i>count</i> is zero all the elements are removed. If <i>count</i> is negativeelements are removed from tail to head, instead to go from head to tailthat is the normal behaviour. So for example LREM with count -2 and_hello_ as value to remove against the list (a,b,c,hello,x,hello,hello) willlave the list (a,b,c,hello,x). The number of removed elements is returnedas an integer, see below for more information aboht the returned value.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer Reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
The number of removed elements if the operation succeeded
-1 if the specified key does not exist
-2 if the specified key does not hold a list value
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LsetCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LSET _key_ _index_ _value_">LSET _key_ _index_ _value_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LsetCommand</h1>
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<h1><a name="LSET _key_ _index_ _value_">LSET _key_ _index_ _value_</a></h1>
<i>Time complexity: O(N) (with N being the length of the list)</i><blockquote>Set the list element at <i>index</i> (see LINDEX for information about the_index_ argument) with the new <i>value</i>. Out of range indexes willgenerate an error. Note that setting the first or last elements ofthe list is O(1).</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>LtrimCommand: Contents</b><br>&nbsp;&nbsp;<a href="#LTRIM _key_ _start_ _end_">LTRIM _key_ _start_ _end_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">LtrimCommand</h1>
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<h1><a name="LTRIM _key_ _start_ _end_">LTRIM _key_ _start_ _end_</a></h1>
<i>Time complexity: O(n) (with n being len of list - len of range)</i><blockquote>Trim an existing list so that it will contain only the specifiedrange of elements specified. Start and end are zero-based indexes.0 is the first element of the list (the list head), 1 the next elementand so on.</blockquote>
<blockquote>For example LTRIM foobar 0 2 will modify the list stored at foobarkey so that only the first three elements of the list will remain.</blockquote>
<blockquote>_start_ and <i>end</i> can also be negative numbers indicating offsetsfrom the end of the list. For example -1 is the last element ofthe list, -2 the penultimate element and so on.</blockquote>
<blockquote>Indexes out of range will not produce an error: if start is overthe end of the list, or start &gt; end, an empty list is left as value.If end over the end of the list Redis will threat it just likethe last element of the list.</blockquote>
<blockquote>Hint: the obvious use of LTRIM is together with LPUSH/RPUSH. For example:</blockquote>
<pre class="codeblock python" name="code">
LPUSH mylist &lt;someelement&gt;
LTRIM mylist 0 99
</pre><blockquote>The above two commands will push elements in the list taking care thatthe list will not grow without limits. This is very useful when usingRedis to store logs for example. It is important to note that when usedin this way LTRIM is an O(1) operation because in the average casejust one element is removed from the tail of the list.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code reply</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="LlenCommand.html">LLEN</a></li><li> <a href="LrangeCommand.html">LRANGE</a></li><li> <a href="LtrimCommand.html">LTRIM</a></li><li> <a href="LdelCommand.html">LDEL</a></li><li> <a href="LindexCommand.html">LINDEX</a></li><li> <a href="LsetCommand.html">LSET</a></li></ul>
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<b>MoveCommand: Contents</b><br>&nbsp;&nbsp;<a href="#MOVE _key_ _dbindex_">MOVE _key_ _dbindex_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">MoveCommand</h1>
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<h1><a name="MOVE _key_ _dbindex_">MOVE _key_ _dbindex_</a></h1>
<blockquote>Move the specified key from the currently selected DB to the specifieddestination DB. Note that this command returns 1 only if the key wassuccessfully moved, and 0 if the target key was already there or if thesource key was not found at all, so it is possible to use MOVE as a lockingprimitive.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/>1 if the key was moved
0 if the key was not moved because already present on the target DB or was not found in the current DB.
-3 if the destination DB is the same as the source DB
-4 if the database index if out of range<h2><a name="See also">See also</a></h2>
<ul><li> <a href="SelectCommand.html">SELECT</a></li><li> <a href="RenameCommand.html">RENAME</a></li></ul>
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<b>ProtocolSpecification: Contents</b><br>&nbsp;&nbsp;<a href="#Protocol Specification">Protocol Specification</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Networking layer">Networking layer</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Simple INLINE commands">Simple INLINE commands</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Bulk commands">Bulk commands</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Bulk replies">Bulk replies</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Bulk reply error reporting">Bulk reply error reporting</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Multi-Bulk replies">Multi-Bulk replies</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Nil elements in Multi-Bulk replies">Nil elements in Multi-Bulk replies</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Multi-Bulk replies errors">Multi-Bulk replies errors</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Status code reply">Status code reply</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Integer reply">Integer reply</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Single line reply">Single line reply</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Multiple commands and pipelining">Multiple commands and pipelining</a>
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<h1 class="wikiname">ProtocolSpecification</h1>
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<h1><a name="Protocol Specification">Protocol Specification</a></h1>The Redis protocol is a compromise between being easy to parse by a computer
and being easy to parse by an human. Before reading this section you are
strongly encouraged to read the &quot;REDIS TUTORIAL&quot; section of this README in order
to get a first feeling of the protocol playing with it by TELNET.<h2><a name="Networking layer">Networking layer</a></h2>A client connects to a Redis server creating a TCP connection to the port 6973.
Every redis command or data transmitted by the client and the server is
terminated by &quot;\r\n&quot; (CRLF).<h2><a name="Simple INLINE commands">Simple INLINE commands</a></h2>The simplest commands are the inline commands. This is an example of a
server/client chat (the server chat starts with S:, the client chat with C:)<br/><br/><pre class="codeblock python" name="code">
C: PING
S: +PONG
</pre>An inline command is a CRLF-terminated string sent to the client. The server
usually replies to inline commands with a single line that can be a number
or a return code.<br/><br/>When the server replies with a status code (that is a one line reply just indicating if the operation succeeded or not), if the first character of the
reply is a &quot;+&quot; then the command succeeded, if it is a &quot;-&quot; then the following
part of the string is an error.<br/><br/>The following is another example of an INLINE command returning an integer:<br/><br/><pre class="codeblock python python" name="code">
C: EXISTS somekey
S: 0
</pre>Since 'somekey' does not exist the server returned '0'.<br/><br/>Note that the EXISTS command takes one argument. Arguments are separated
simply by spaces.<h2><a name="Bulk commands">Bulk commands</a></h2>A bulk command is exactly like an inline command, but the last argument
of the command must be a stream of bytes in order to send data to the server.
the &quot;SET&quot; command is a bulk command, see the following example:<br/><br/><pre class="codeblock python python python" name="code">
C: SET mykey 6
C: foobar
S: +OK
</pre>The last argument of the commnad is '6'. This specify the number of DATA
bytes that will follow (note that even this bytes are terminated by two
additional bytes of CRLF).<br/><br/>All the bulk commands are in this exact form: instead of the last argument
the number of bytes that will follow is specified, followed by the bytes,
and CRLF. In order to be more clear for the programmer this is the string
sent by the client in the above sample:<br/><br/><blockquote>&quot;SET mykey 6\r\nfoobar\r\n&quot;</blockquote>
<h2><a name="Bulk replies">Bulk replies</a></h2>The server may reply to an inline or bulk command with a bulk reply. See
the following example:<br/><br/><pre class="codeblock python python python python" name="code">
C: GET mykey
S: 6
S: foobar
</pre>A bulk reply is very similar to the last argument of a bulk command. The
server sends as the first line the number of bytes of the actual reply
followed by CRLF, then the bytes are sent followed by additional two bytes
for the final CRLF. The exact sequence sent by the server is:<br/><br/><blockquote>&quot;6\r\nfoobar\r\n&quot;</blockquote>
If the requested value does not exist the bulk reply will use the special
value 'nil' instead to send the line containing the number of bytes to read.
This is an example:<br/><br/><pre class="codeblock python python python python python" name="code">
C: GET nonexistingkey
S: nil
</pre>The client library API should not return an empty string, but a nil object.
For example a Ruby library should return 'nil' while a C library should return
NULL.<h2><a name="Bulk reply error reporting">Bulk reply error reporting</a></h2>Bulk replies can signal errors, for example trying to use GET against a list
value is not permitted. Bulk replies use a negative bytes count in order to
signal an error. An error string of ABS(bytes_count) bytes will follow. See
the following example:<br/><br/><pre class="codeblock python python python python python python" name="code">
S: GET alistkey
S: -38
S: -ERR Requested element is not a string
</pre>-38 means: sorry your operation resulted in an error, but a 38 bytes string
that explains this error will follow. Client APIs should abort on this kind
of errors, for example a PHP client should call the die() function.<br/><br/>The following commands reply with a bulk reply: GET, KEYS, LINDEX, LPOP, RPOP<h2><a name="Multi-Bulk replies">Multi-Bulk replies</a></h2>Commands similar to LRANGE needs to return multiple values (every element
of the list is a value, and LRANGE needs to return more than a single element). This is accomplished using multiple bulk writes,
prefixed by an initial line indicating how many bulk writes will follow.
Example:<br/><br/><pre class="codeblock python python python python python python python" name="code">
C: LRANGE mylist 0 3
S: 4
S: 3
S: foo
S: 3
S: bar
S: 5
S: Hello
S: 5
S: World
</pre>The first line the server sent is &quot;4\r\n&quot; in order to specify that four bulk
write will follow. Then every bulk write is transmitted.<br/><br/>If the specified key does not exist instead of the number of elements in the
list, the special value 'nil' is sent. Example:<br/><br/><pre class="codeblock python python python python python python python python" name="code">
C: LRANGE nokey 0 1
S: nil
</pre>A client library API SHOULD return a nil object and not an empty list when this
happens. This makes possible to distinguish between empty list and non existing ones.<h2><a name="Nil elements in Multi-Bulk replies">Nil elements in Multi-Bulk replies</a></h2>Single elements of a multi bulk reply may have -1 length, in order to signal that this elements are missing and not empty strings. This can happen with the SORT command when used with the GET <i>pattern</i> option when the specified key is missing. Example of a multi bulk reply containing an empty element:<br/><br/><pre class="codeblock python python python python python python python python python" name="code">
S: 3
S: 3
S: foo
S: -1
S: 3
S: bar
</pre>The second element is nul. The client library should return something like this:<br/><br/><pre class="codeblock python python python python python python python python python python" name="code">
[&quot;foo&quot;,nil,&quot;bar&quot;]
</pre><h2><a name="Multi-Bulk replies errors">Multi-Bulk replies errors</a></h2>Like bulk reply errors Multi-bulk reply errors are reported using a negative
count. Example:<br/><br/><pre class="codeblock python python python python python python python python python python python" name="code">
C: LRANGE stringkey 0 1
S: -38
S: -ERR Requested element is not a string
</pre>The following commands reply with a multi-bulk reply: LRANGE, LINTER<br/><br/>Check the Bulk replies errors section for more information.<h2><a name="Status code reply">Status code reply</a></h2>As already seen a status code reply is in the form of a single line string
terminated by &quot;\r\n&quot;. For example:<br/><br/><pre class="codeblock python python python python python python python python python python python python" name="code">
+OK
</pre>and<br/><br/><pre class="codeblock python python python python python python python python python python python python python" name="code">
-ERR no suck key
</pre>are two examples of status code replies. The first character of a status code reply is always &quot;+&quot; or &quot;-&quot;.<br/><br/>The following commands reply with a status code reply:
PING, SET, SELECT, SAVE, BGSAVE, SHUTDOWN, RENAME, LPUSH, RPUSH, LSET, LTRIM<h2><a name="Integer reply">Integer reply</a></h2>This type of reply is just a CRLF terminated string representing an integer. For example &quot;0\r\n&quot;, or &quot;1000\r\n&quot; are integer replies.<br/><br/>With commands like INCR or LASTSAVE using the integer reply to actually return a value there is no special meaning for the returned integer. It is just an incremental number for INCR, a UNIX time for LASTSAVE and so on.<br/><br/>Some commands like EXISTS will return 1 for true and 0 for false.<br/><br/>Other commands like SADD, SREM and SETNX will return 1 if the operation was actually done, 0 otherwise, and <b>a negative value</b> if the operation is invalid (for example SADD against a non-set value), accordingly to this table:
<pre class="codeblock python python python python python python python python python python python python python python" name="code">
-1 no such key
-2 operation against the a key holding a value of the wrong type
-3 source and destiantion objects/dbs are the same
-4 argument out of range
</pre>
In all this cases it is mandatory that the client raises an error instead to pass the negative value to the caller. Please check the commands documentation for the exact behaviour.<br/><br/>The following commands will reply with an integer reply: SETNX, DEL, EXISTS, INCR, INCRBY, DECR, DECRBY, DBSIZE, LASTSAVE, RENAMENX, MOVE, LLEN, SADD, SREM, SISMEMBER, SCARD<br/><br/>The commands that will never return a negative integer (commands that can't fail) are: INCR, DECR, INCRBY, DECRBY, LASTSAVE, EXISTS, SETNX, DEL, DBSIZE.<h2><a name="Single line reply">Single line reply</a></h2>This replies are just single line strings terminated by CRLF. Only two commands reply in this way currently, RANDOMKEY and TYPE.<h2><a name="Multiple commands and pipelining">Multiple commands and pipelining</a></h2>A client can use the same connection in order to issue multiple commands.
Pipelining is supported so multiple commands can be sent with a single
write operation by the client, it is not needed to read the server reply
in order to issue the next command. All the replies can be read at the end.<br/><br/>Usually Redis server and client will have a very fast link so this is not
very important to support this feature in a client implementation, still
if an application needs to issue a very large number of commands in short
time to use pipelining can be much faster.<br/><br/>
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<b>QuitCommand: Contents</b><br>&nbsp;&nbsp;<a href="#Quit">Quit</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a>
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<h1 class="wikiname">QuitCommand</h1>
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<h1><a name="Quit">Quit</a></h1><blockquote>Ask the server to silently close the connection.</blockquote>
<h2><a name="Return value">Return value</a></h2>None. The connection is closed as soon as the QUIT command is received.
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<b>README: Contents</b><br>&nbsp;&nbsp;<a href="#Introduction">Introduction</a><br>&nbsp;&nbsp;<a href="#Beyond key-value databases">Beyond key-value databases</a><br>&nbsp;&nbsp;<a href="#What are the differences between Redis and Memcached?">What are the differences between Redis and Memcached?</a><br>&nbsp;&nbsp;<a href="#What are the differences between Redis and Tokyo Cabinet / Tyrant?">What are the differences between Redis and Tokyo Cabinet / Tyrant?</a><br>&nbsp;&nbsp;<a href="#Does Redis support locking?">Does Redis support locking?</a><br>&nbsp;&nbsp;<a href="#Multiple databases support">Multiple databases support</a><br>&nbsp;&nbsp;<a href="#Redis Data Types">Redis Data Types</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Implementation Details">Implementation Details</a><br>&nbsp;&nbsp;<a href="#Redis Tutorial">Redis Tutorial</a><br>&nbsp;&nbsp;<a href="#License">License</a><br>&nbsp;&nbsp;<a href="#Credits">Credits</a>
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<h1><a name="Introduction">Introduction</a></h1>Redis is a database. To be more specific redis is a very simple database
implementing a dictionary where keys are associated with values. For example
I can set the key &quot;surname_1992&quot; to the string &quot;Smith&quot;.<br/><br/>Redis takes the whole dataset in memory, but the dataset is persistent
since from time to time Redis writes a dump of the dataset on disk asynchronously. The dump is loaded every time the server is restarted. This means that if a system crash occurs the last few queries can get lost (that is acceptable in many applications), so we supported master-slave replication from the early days.<h1><a name="Beyond key-value databases">Beyond key-value databases</a></h1>In most key-value databases keys and values are simple strings. In Redis keys are just strings too, but the associated values can be Strings, Lists and Sets, and there are commands to perform complex atomic operations against this data types, so you can think at Redis as a data structures server.<br/><br/>For example you can append elements to a list stored at the key &quot;mylist&quot; using the LPUSH or RPUSH operation in O(1). Later you'll be able to get a range of elements with LRANGE or trim the list with LTRIM. Sets are very flexible too, it is possible to add and remove elements from Sets (unsorted collections of strings), and then ask for server-side intersection of Sets.<br/><br/>All this features, the support for sorting Lists and Sets, allow to use Redis as the sole DB for your scalable application without the need of any relational database. <a href="TwitterAlikeExample.html">We wrote a simple Twitter clone in PHP + Redis</a> to show a real world example, the link points to an article explaining the design and internals in very simple words.<h1><a name="What are the differences between Redis and Memcached?">What are the differences between Redis and Memcached?</a></h1>In the following ways:<br/><br/><ul><li> Memcached is not persistent, it just holds everything in memory without saving since its main goal is to be used as a cache. Redis instead can be used as the main DB for the application. We <a href="TwitterAlikeExample.html">wrote a simple Twitter clone</a> using only Redis as database.</li></ul>
<ul><li> Like memcached Redis uses a key-value model, but while keys can just be strings, values in Redis can be lists and sets, and complex operations like intersections, set/get n-th element of lists, pop/push of elements, can be performed against sets and lists. It is possible to use lists as message queues.</li></ul>
<h1><a name="What are the differences between Redis and Tokyo Cabinet / Tyrant?">What are the differences between Redis and Tokyo Cabinet / Tyrant?</a></h1>Redis and Tokyo can be used for the same applications, but actually they are <b>ery</b> different beasts:<br/><br/><ul><li> Tokyo is purely key-value, everything beyond key-value storing of strings is delegated to an embedded Lua interpreter. AFAIK there is no way to guarantee atomicity of operations like pushing into a list, and every time you want to have data structures inside a Tokyo key you have to perform some kind of object serialization/de-serialization.</li></ul>
<ul><li> Tokyo stores data on disk, synchronously, this means you can have datasets bigger than memory, but that under load, like every kind of process that relay on the disk I/O for speed, the performances may start to degrade. With Redis you don't have this problems but you have another problem: the dataset in every single server must fit in your memory.</li></ul>
<ul><li> Redis is generally an higher level beast in the operations supported. Things like SORTing, Server-side set-intersections, can't be done with Tokyo. But Redis is not an on-disk DB engine like Tokyo: the latter can be used as a fast DB engine in your C project without the networking overhead just linking to the library. Still remember that in many scalable applications you need multiple servers talking with multiple servers, so the server-client model is almost always needed.</li></ul>
<h1><a name="Does Redis support locking?">Does Redis support locking?</a></h1>No, the idea is to provide atomic primitives in order to make the programmer
able to use redis with locking free algorithms. For example imagine you have
10 computers and 1 redis server. You want to count words in a very large text.
This large text is split among the 10 computers, every computer will process
its part and use Redis's INCR command to atomically increment a counter
for every occurrence of the word found.<br/><br/>INCR/DECR are not the only atomic primitives, there are others like PUSH/POP
on lists, POP RANDOM KEY operations, UPDATE and so on. For example you can
use Redis like a Tuple Space (<a href="http://en.wikipedia.org/wiki/Tuple_space" target="_blank">http://en.wikipedia.org/wiki/Tuple_space</a>) in
order to implement distributed algorithms.<br/><br/>(News: locking with key-granularity is now planned)<h1><a name="Multiple databases support">Multiple databases support</a></h1>Another synchronization primitive is the support for multiple DBs. By default DB 0 is selected for every new connection, but using the SELECT command it is possible to select a different database. The MOVE operation can move an item from one DB to another atomically. This can be used as a base for locking free algorithms together with the 'RANDOMKEY' or 'POPRANDOMKEY' commands.<h1><a name="Redis Data Types">Redis Data Types</a></h1>Redis supports the following three data types as values:<br/><br/><ul><li> Strings: just any sequence of bytes. Redis strings are binary safe so they can not just hold text, but images, compressed data and everything else.</li><li> Lists: lists of strings, with support for operations like append a new string on head, on tail, list length, obtain a range of elements, truncate the list to a given length, sort the list, and so on.</li><li> Sets: an unsorted set of strings. It is possible to add or delete elements from a set, to perform set intersection, union, subtraction, and so on.</li></ul>
Values can be Strings, Lists or Sets. Keys can be a subset of strings not containing newlines (&quot;\n&quot;) and spaces (&quot; &quot;).<br/><br/>Note that sometimes strings may hold numeric vaules that must be parsed by
Redis. An example is the INCR command that atomically increments the number
stored at the specified key. In this case Redis is able to handle integers
that can be stored inside a 'long long' type, that is a 64-bit signed integer.<h2><a name="Implementation Details">Implementation Details</a></h2>Strings are implemented as dynamically allocated strings of characters.
Lists are implemented as doubly linked lists with cached length.
Sets are implemented using hash tables that use chaining to resolve collisions.<h1><a name="Redis Tutorial">Redis Tutorial</a></h1>(note, you can skip this section if you are only interested in &quot;formal&quot; doc.)<br/><br/>Later in this document you can find detailed information about Redis commands,
the protocol specification, and so on. This kind of documentation is useful
but... if you are new to Redis it is also BORING! The Redis protocol is designed
so that is both pretty efficient to be parsed by computers, but simple enough
to be used by humans just poking around with the 'telnet' command, so this
section will show to the reader how to play a bit with Redis to get an initial
feeling about it, and how it works.<br/><br/>To start just compile redis with 'make' and start it with './redis-server'.
The server will start and log stuff on the standard output, if you want
it to log more edit redis.conf, set the loglevel to debug, and restart it.<br/><br/>You can specify a configuration file as unique parameter:<br/><br/><blockquote>./redis-server /etc/redis.conf</blockquote>
This is NOT required. The server will start even without a configuration file
using a default built-in configuration.<br/><br/>Now let's try to set a key to a given value:<br/><br/><pre class="codeblock python" name="code">
$ telnet localhost 6379
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
SET foo 3
bar
+OK
</pre>The first line we sent to the server is &quot;set foo 3&quot;. This means &quot;set the key
foo with the following three bytes I'll send you&quot;. The following line is
the &quot;bar&quot; string, that is, the three bytes. So the effect is to set the
key &quot;foo&quot; to the value &quot;bar&quot;. Very simple!<br/><br/>(note that you can send commands in lowercase and it will work anyway,
commands are not case sensitive)<br/><br/>Note that after the first and the second line we sent to the server there
is a newline at the end. The server expects commands terminated by &quot;\r\n&quot;
and sequence of bytes terminated by &quot;\r\n&quot;. This is a minimal overhead from
the point of view of both the server and client but allows us to play with
Redis with the telnet command easily.<br/><br/>The last line of the chat between server and client is &quot;+OK&quot;. This means
our key was added without problems. Actually SET can never fail but
the &quot;+OK&quot; sent lets us know that the server received everything and
the command was actually executed.<br/><br/>Let's try to get the key content now:<br/><br/><pre class="codeblock python python" name="code">
GET foo
3
bar
</pre>Ok that's very similar to 'set', just the other way around. We sent &quot;get foo&quot;,
the server replied with a first line that is just a number of bytes the value
stored at key contained, followed by the actual bytes. Again &quot;\r\n&quot; are appended
both to the bytes count and the actual data.<br/><br/>What about requesting a non existing key?<br/><br/><pre class="codeblock python python python" name="code">
GET blabla
nil
</pre>When the key does not exist instead of the length just the &quot;nil&quot; string is sent.
Another way to check if a given key exists or not is indeed the EXISTS command:<br/><br/><pre class="codeblock python python python python" name="code">
EXISTS nokey
0
EXISTS foo
1
</pre>As you can see the server replied '0' the first time since 'nokey' does not
exist, and '1' for 'foo', a key that actually exists.<br/><br/>Ok... now you know the basics, read the <a href="CommandReference.html">REDIS COMMAND REFERENCE</a> section to
learn all the commands supported by Redis and the <a href="ProtocolSpecification.html">PROTOCOL SPECIFICATION</a>
section for more details about the protocol used if you plan to implement one
for a language missing a decent client implementation.<h1><a name="License">License</a></h1>Redis is released under the BSD license. See the COPYING file for more information.<h1><a name="Credits">Credits</a></h1>Redis is written and maintained by Salvatore Sanfilippo, Aka 'antirez'.<br/><br/>Enjoy,
antirez
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<b>RandomkeyCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RANDOMKEY">RANDOMKEY</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1><a name="RANDOMKEY">RANDOMKEY</a></h1>
<i>Time complexity: O(1)</i><blockquote>Return a randomly selected key from the currently selected DB.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Singe line reply</a>, specifically the randomly selected key or an empty string is the database is empty.<h2><a name="See also">See also</a></h2>
<ul><li> <a href="KeysCommand.html">KEYS</a></li></ul>
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<b>RenameCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RENAME _oldkey_ _newkey_">RENAME _oldkey_ _newkey_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">RenameCommand</h1>
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<h1><a name="RENAME _oldkey_ _newkey_">RENAME _oldkey_ _newkey_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Atomically renames the key <i>oldkey</i> to <i>newkey</i>. If the source anddestination name are the same an error is returned. If <i>newkey</i>already exists it is overwritten.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Status code repy</a><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RenamenxCommand.html">RENAMENX</a> if you don't want overwrite the destionation key if it exists.</li></ul>
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<b>RenamenxCommand: Contents</b><br>&nbsp;&nbsp;<a href="#RENAMENX _oldkey_ _newkey_">RENAMENX _oldkey_ _newkey_</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Return value">Return value</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#See also">See also</a>
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<h1 class="wikiname">RenamenxCommand</h1>
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<h1><a name="RENAMENX _oldkey_ _newkey_">RENAMENX _oldkey_ _newkey_</a></h1>
<i>Time complexity: O(1)</i><blockquote>Rename <i>oldkey</i> into <i>newkey</i> but fails if the destination key <i>newkey</i> already exists.</blockquote>
<h2><a name="Return value">Return value</a></h2><a href="ReplyTypes.html">Integer reply</a>, specifically:<br/><br/><pre class="codeblock python" name="code">
1 if the key was renamed
0 if the target key already exist
-1 if the source key does not exist
-3 if source and destination keys are the same
</pre><h2><a name="See also">See also</a></h2>
<ul><li> <a href="RenameCommand.html">RENAME</a> is like RENAMENX but overwrite existing destionation key.</li></ul>
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