Memcache::get

(PECL memcache >= 0.2.0)

Memcache::get — 从服务端检回一个元素

说明

Memcache::get ( string $key , int &$flags = ? ) : string

Memcache::get ( array $keys , array &$flags = ? ) : array

如果服务端之前有以key作为key存储的元素，Memcache::get()方法此时返回之前存储的值。

你可以给Memcache::get()方法传递一个数组（多个key）来获取一个数组的元素值，返回的数组仅仅包含从服务端查找到的key-value对。

参数

key: 要获取值的key或key数组。
flags: 如果给定这个参数（以引用方式传递），该参数会被写入一些key对应的信息。这些标记和Memcache::set()方法中的同名参数意义相同。用int值的低位保留了pecl/memcache的内部用法（比如：用来说明压缩和序列化状态）。（译注：最后一位表明是否序列化，倒数第二位表明是否经过压缩，比如：如果此值为1表示经过序列化，但未经过压缩，2表明压缩而未序列化，3表明压缩并且序列化，0表明未经过压缩和序列化，具体算法可查找linux文件权限算法相关资料）

返回值

返回key对应的存储元素的字符串值或者在失败或key未找到的时候返回false。

范例

Example #1 Memcache::get() 示例


<?php

/* procedural API */
$memcache_obj = memcache_connect('memcache_host', 11211);
$var = memcache_get($memcache_obj, 'some_key');

/* OO API */
$memcache_obj = new Memcache;
$memcache_obj->connect('memcache_host', 11211);
$var = $memcache_obj->get('some_key');

/* 
你同样可以使用数组key作为参数，如果某个元素没有在服务端发现，结果数组中将不会包含这些key。
*/

/* procedural API */
$memcache_obj = memcache_connect('memcache_host', 11211);
$var = memcache_get($memcache_obj, Array('some_key', 'another_key'));

/* OO API */
$memcache_obj = new Memcache;
$memcache_obj->connect('memcache_host', 11211);
$var = $memcache_obj->get(Array('some_key', 'second_key'));

?>

User Contributed Notes

csongor at halmai dot hu 07-Oct-2014 04:27


Avoid reading too many values from memcahce. Each get() consumes some memory. You should cache the values instead, once they are read. Illustration of bad practice:



<?php   // reading from memcache leaks



    $m = new Memcache();

    $m -> connect( "localhost", "11211" );

    $m -> add("foo", "bar");



    for(;;) {  // this "endless" loop will finish because it eats up all the memory

        $res = $m -> get("foo");

        print memory_get_usage()."\n";  // this writes bigger and bigger numbers

    }

a dot karabiowski at gmx dot net 27-Jan-2014 09:19


Signature is not correct.



<?php 

$memcache = new Memcache();

$memcache->connect('localhost', 11211);

class Test { public $property = "testvalue"; }

$test = new Test();

$memcache->set("asdf", $test);

var_dump($memcache->get("asdf"));

/* will return the object, not the string:

    class Test#3 (1) {

      public $property =>

      string(9) "testvalue"

    }

*/

?>

bijay dot rungta at gmail dot com 21-May-2013 06:31


Note that if you include spaces in your keys when saving Data and use array of keys to get the Data, The returned array will replace spaces with underscores in the keys. 



<?php



$memcache = new Memcache;

$memcache->connect('localhost');

$memcache->set('my-key', 'value1', 0, 300);

$memcache->set('key with space', 'value 2', 0, 300);



print_r($memcache->get(array('my-key', 'key with space'))); // Array ( [my-key] => value1 [key_with_space] => value 2 )



?>



Memcache replaces spaces with underscores when saving, it does so when doing a get too, but when you do a get with single key (string) you don't notice this as it merely returns the value. But when you do a get for array of keys, you would expect the same keys in the returned array but it replaces spaces by underscores in them.

clover at fromru dot com 27-Apr-2013 12:14


$flags stays untouched if $key was not found on the server, it's helpfull to determine if bool(false) was stored:



<?php



$memcache = new Memcache();



$memcache->set('test', false); // 

$flags = false;

var_dump($memcache->get('test', $flags)); // bool(false)

var_dump($flags); // int(256) - changed to int



$memcache->delete('test');



$flags = false;

var_dump($memcache->get('test', $flags)); // bool(false)

var_dump($flags); // bool(false) - untouched



?>

Michael Brenden 17-Feb-2011 02:46


Beware, if there's a backslash present in the key name then the results are unpredictable and random.



I was generating keys like this:



$mc_key = get_called_class(). $_COOKIE['crumb'];



This works fine when get_called_class() returns CLASSNAME.



But then I began using namespaces, and get_class_class() of course returned NAMESPACE\CLASSNAME



Well that backslash sends Memcache into quite the tizzy.

No errors, mind you, just insanity.

janis at unrepublic dot com 22-Mar-2010 02:00


For me it was the case that if such key doesn't exist, null is returned not false.

nate 14-Oct-2008 08:18


Be aware that when using the multi-key version, Memcache::get returns bool false if no servers are configured for the pool (and possibly if other errors occur as well while attempting to fetch). Also, Memcache class throws annoying warnings on every get/set/delete-type calls if you have no servers added to the pool.





The following snippet var_dump's bool false, not an empty array like you might expect.





<?php


$cache = new Memcache;





// no $cache->addServer calls (for example,


due to temporarily disabling use of cache)





// use @ symbol to ignore warning





var_dump(


    @$cache->get(array('one', 'two'))


);


?>

jakub dot lopuszanski at nasza-klasa dot pl 07-Jul-2008 07:39


If deserialization fails for some reason, that is when memcache server returned flag 1 set, but the value was not a correctly serialized PHP data,


then Memcache::get acts in a following way:





If it was called with a single key to retrieve, then a warning is raised, but since it was not actually a bug of a server, the warning says something confusing like "Memcached Server Error: null" and the function returns bool(false).





If it was called by passing an array (even with a single element in it), then the warning is not raised and the resulting array contains a value bool(false).





Since there are some buffer overrun bugs present in Memcached Server, which from time to time cause overwriting of [part of] data and therefore rendering it impossible to deserialize, make sure to check if the result of Memcache::get contains only string, or deserialized structure. If the result is bool,dobule or long, then something went wrong.