Memcache::set

memcache_set

(PECL memcache >= 0.2.0)

Memcache::set -- memcache_set — Almacena datos en el servidor de caché

Descripción

Memcache::set(
    string $key,
    mixed $var,
    int $flag = ?,
    int $expire = ?
): bool

memcache_set(
    Memcache $memcache,
    string $key,
    mixed $var,
    int $flag = ?,
    int $expire = ?
): bool

Memcache::set() almacena el elemento var con la clave key en el servidor de caché. El parámetro expire representa el tiempo de expiración en segundos del elemento. Si vale 0, el elemento no expirará nunca (aunque el servidor de caché no garantiza que este elemento siempre estará almacenado, puede ser eliminado de la caché para hacer espacio para otros elementos). Puede utilizarse la constante MEMCACHE_COMPRESSED como valor del parámetro flag si se desea utilizar la compresión en tiempo real (utilizando la biblioteca zlib).

Nota:
Tenga en cuenta que los recursos (es decir, identificadores de archivos o conexiones) no pueden almacenarse en la caché, ya que no pueden ser representados linealmente.

Parámetros

key: La clave que se asociará con el elemento.
var: La variable a registrar. Los strings y los integers se registran como tales, los demás tipos se registran de manera serializada.
flag: Utilice MEMCACHE_COMPRESSED para registrar el elemento comprimido (utiliza zlib).
expire: Tiempo de expiración para el elemento. Si es igual a 0, el elemento no expirará. También puede utilizarse un timestamp Unix o un número de segundos a partir de la fecha actual, pero en este último caso, el número de segundos no debe exceder 2592000 (30 días).

Valores devueltos

Esta función retorna true en caso de éxito o false si ocurre un error.

Ejemplos

Ejemplo #1 Ejemplo con Memcache::set()

<?php
/* API procedimental */

/* conexión al servidor de caché */
$memcache_obj = memcache_connect('memcache_host', 11211);

/*
define el valor del elemento identificado por la clave 'var_key' ;
utilización del valor 0 para el flag ;
la compresión no se utiliza ;
el tiempo de expiración es de 30 segundos
*/
memcache_set($memcache_obj, 'var_key', 'algunas variables', 0, 30);

echo memcache_get($memcache_obj, 'var_key');

?>

Ejemplo #2 Ejemplo con Memcache::set()

<?php
/* API orientada a objetos */

$memcache_obj = new Memcache;

/* conexión al servidor de caché */
$memcache_obj->connect('memcache_host', 11211);

/*
define el valor del elemento identificado por la clave 'var_key' ;
utilización de la compresión en tiempo real ;
el tiempo de expiración es de 50 segundos
*/
$memcache_obj->set('var_key', 'algunas variables grandes', MEMCACHE_COMPRESSED, 50);

echo $memcache_obj->get('var_key');

?>

Ver también

Memcache::add() - Añade un elemento en el servidor
Memcache::replace() - Remplaza el valor de un elemento existente

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User Contributed Notes 9 notes

down

Sc00bz ¶

18 years ago

This is just two minor things about memcache that might not be perfectly clear, the limits on key and data sizes and what happen to flags in the memcache protocol.



* There is a max key size of 250 anything bigger gets truncated. There is also a (1MB - 42 bytes) limit on the data.



* In the memcache protocol there is a 16bit, 32bit in newer version, flag that you can set to whatever you want because memcache doesn't do anything with the flags. The php api doesn't let you get the flags because php uses the flags for php's own use such as "MEMCACHE_COMPRESSED" and I decided to test if it was doing something because it wasn't part of the memcache protocol.



<?php

$memcache = new Memcache();

$memcache->connect("127.0.0.1", 11211);



// Since memcache truncates the keys at 250 bytes both the get "250 a's" and "251 a's" will find the key in the cache

echo "*** Truncate key test ***<br>";

echo "set 251: " . ($memcache->set(str_repeat("a", 251), "value", 0, 1) ? "t" : "f") . "<br>";



echo "get 249: " . (($ret = $memcache->get(str_repeat("a", 249))) !== false ? "'$ret'" : "f") . "<br>";

echo "get 250: " . (($ret = $memcache->get(str_repeat("a", 250))) !== false ? "'$ret'" : "f") . "<br>";

echo "get 251: " . (($ret = $memcache->get(str_repeat("a", 251))) !== false ? "'$ret'" : "f") . "<br>";

echo "delete: " . ($memcache->delete(str_repeat("a", 250)) ? "t" : "f") . "<br><br>";



echo "*** Compress value test ***<br>";

echo "set 1024*1024-42: " . ($memcache->set("test", str_repeat("a", 1024*1024-42), 0, 1) ? "t" : "f") . "<br>";

echo "set 1024*1024-41: " . ($memcache->set("test", str_repeat("a", 1024*1024-41), 0, 1) ? "t" : "f") . "<br>";

echo "set 1024*1024 compressed: " . ($memcache->set("test", str_repeat("a", 1024*1024), MEMCACHE_COMPRESSED, 1) ? "t" : "f") . "<br>";

echo "delete: " . ($memcache->delete("test") ? "t" : "f") . "<br>";

$memcache->close();

?>



Output:

*** Truncate key test ***

set 251: t

get 249: f

get 250: 'value'

get 251: 'value'

delete: t



*** Compress value test ***

set 1024*1024-42: t

set 1024*1024-41: f

set 1024*1024 compressed: t

delete: t

down

wbonde at yakabod dot com ¶

14 years ago

The max time for expiration (without having to worry about deletions when necessary as with 0 seconds) is 2,592,000 seconds (30 days). 

Specifying an expiration value above that will return false, but will NOT throw in error so it is easy to miss.

down

argyleblanket ¶

17 years ago

Using set more than once for the same key seems to have unexpected results - it does not behave as a "replace," but instead seems to "set" more than one value for the same key.  "get" may return any of the values.



This was tested on a multiple-server setup - behaviour may be different if you only have one server.



Remedy is to use a combination of replace and set:



<?php

$result = $memcache->replace( $key, $var );

if( $result == false )

{

    $result = $memcache->set( $key, $var );

}

?>

down

Stephen from veedow.com ¶

17 years ago

I ran into problems using the MEMCACHE_COMPRESSED flag when storing small amounts of data, such as an integers.



For expample.



<?php

Memcache::set('integer', 123456, MEMCACHE_COMPRESSED);

//would return true



Memcache::get('integer');

//would return false

?>



This problem went away when I removed the MEMCACHE_COMPRESSED flag for values that were small.

down

duerra at nospam dot yahoo dot com ¶

14 years ago

If you're interested in using compression, please note that, at least for PHP version 5.3.2 and Memcache version 3.0.4, when retrieving a key who's value is a numeric or boolean type, PHP throws a notice of the following:

Message: MemcachePool::get(): Failed to uncompress data

The way around this is to test your variable type before setting or adding it to Memcache, or even cast it as a string.  

<?php
$key = 'mc_key';
$value = 12345;
$compress = is_bool($value) || is_int($value) || is_float($value) ? false : MEMCACHE_COMPRESSED;

$mc= new Memcache;
$mc->connect('localhost', 11211);
$mc->set($key, $value, $compress);

echo $mc->get($key);

//Alternative is to cast the variable
$value = is_scalar($value) ? (string)$value : $value;
$mc->set($key, $value, MEMCACHE_COMPRESSED);
?>

down

winmutt ¶

6 years ago

The note here about replace and set is no longer valid in my testing. You can call set as many times as you want on the same key and reliably get the last written value. I tested this with 3 memcache nodes over 10000 keys.

down

jcastromail at yahoo dot es ¶

7 years ago

If you get the next message

"The lowest two bytes of the flags array is reserved for pecl/memcache internal use"

Then try the next operations:
a) try to use Memcached instead of Memcache.
b) switch the compressed value
  $memcache->set($key,$value,MEMCACHE_COMPRESSED)
  or
  $memcache->set($key,$value,0)

down

-1

effeesse gmail com ¶

15 years ago

if you want to cache an image created on-the-fly you can do:



<?php

ob_start();

imagepng($image);

$memcache->set("my_image", ob_get_contents(), false, $cache_time);

ob_end_clean();

?>



then you could access the chached image as simple variable:

<?php $my_image = $memcache->get("my_image"); ?>



so, in short, you have to buffer the output

down

-4

aamthor at advertzoom dot de ¶

12 years ago

to put some things right:

max expiration time: RTFM, it's written here.

max amount of data: almost unlimited as long as your server can bear it.

speed and pace: 
well, thats another thing. We had a couple of data records which for application reasons must be kept in memory. Since the bunch of data is big and doesn't change very often, we considered caching it to memcache instead of retrieving it from the DB each and every time.

This isn't a general advice nor any quality statement, but we did a couple of tests with serialized arrays (50 MB), compressed and uncompressed and it turned out that in our particular scenario, memcache is much slower than the DB (mySql).

In general, one can not predict on the behavior of memcache in certain scenarios but always need to make some testing and benchmarking upfront before starting to deploy things to a live system.

Despite of the tests above, we are still using memcache for session caching instead of file system, since there are certain other things to consider and the amount of data is always small (few KB)

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