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(PECL memcache >= 0.2.0)

Memcache::setStore data at the server


bool Memcache::set ( string $key , mixed $var [, int $flag [, int $expire ]] )

Memcache::set() stores an item var with key on the memcached server. Parameter expire is expiration time in seconds. If it's 0, the item never expires (but memcached server doesn't guarantee this item to be stored all the time, it could be deleted from the cache to make place for other items). You can use MEMCACHE_COMPRESSED constant as flag value if you want to use on-the-fly compression (uses zlib).


Remember that resource variables (i.e. file and connection descriptors) cannot be stored in the cache, because they cannot be adequately represented in serialized state.

Also you can use memcache_set() function.



The key that will be associated with the item.


The variable to store. Strings and integers are stored as is, other types are stored serialized.


Use MEMCACHE_COMPRESSED to store the item compressed (uses zlib).


Expiration time of the item. If it's equal to zero, the item will never expire. You can also use Unix timestamp or a number of seconds starting from current time, but in the latter case the number of seconds may not exceed 2592000 (30 days).

Return Values

Returns TRUE on success or FALSE on failure.


Example #1 Memcache::set() example

/* procedural API */

/* connect to memcached server */
$memcache_obj memcache_connect('memcache_host'11211);

set value of item with key 'var_key'
using 0 as flag value, compression is not used
expire time is 30 seconds
memcache_set($memcache_obj'var_key''some variable'030);



Example #2 Memcache::set() example

/* OO API */

$memcache_obj = new Memcache;

/* connect to memcached server */

set value of item with key 'var_key', using on-the-fly compression
expire time is 50 seconds
$memcache_obj->set('var_key''some really big variable'MEMCACHE_COMPRESSED50);



See Also

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User Contributed Notes 8 notes

9 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.

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

"get 249: " . (($ret = $memcache->get(str_repeat("a", 249))) !== false ? "'$ret'" : "f") . "<br>";
"get 250: " . (($ret = $memcache->get(str_repeat("a", 250))) !== false ? "'$ret'" : "f") . "<br>";
"get 251: " . (($ret = $memcache->get(str_repeat("a", 251))) !== false ? "'$ret'" : "f") . "<br>";
"delete: " . ($memcache->delete(str_repeat("a", 250)) ? "t" : "f") . "<br><br>";

"*** Compress value test ***<br>";
"set 1024*1024-42: " . ($memcache->set("test", str_repeat("a", 1024*1024-42), 0, 1) ? "t" : "f") . "<br>";
"set 1024*1024-41: " . ($memcache->set("test", str_repeat("a", 1024*1024-41), 0, 1) ? "t" : "f") . "<br>";
"set 1024*1024 compressed: " . ($memcache->set("test", str_repeat("a", 1024*1024), MEMCACHE_COMPRESSED, 1) ? "t" : "f") . "<br>";
"delete: " . ($memcache->delete("test") ? "t" : "f") . "<br>";

*** 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
wbonde at yakabod dot com
6 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.
duerra at nospam dot yahoo dot com
6 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. 

= '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);


//Alternative is to cast the variable
$value = is_scalar($value) ? (string)$value : $value;
$mc->set($key, $value, MEMCACHE_COMPRESSED);
8 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:

= $memcache->replace( $key, $var );
$result == false )
$result = $memcache->set( $key, $var );
Stephen from
9 years ago
I ran into problems using the MEMCACHE_COMPRESSED flag when storing small amounts of data, such as an integers.

For expample.

::set('integer', 123456, MEMCACHE_COMPRESSED);
//would return true

//would return false

This problem went away when I removed the MEMCACHE_COMPRESSED flag for values that were small.
effeesse gmail com
7 years ago
if you want to cache an image created on-the-fly you can do:

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

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
aamthor at advertzoom dot de
4 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)
jakub dot lopuszanski at nasza-klasa dot pl
9 years ago
The lowest byte of the int is reserved for pecl/memcache internal usage (e.g. to indicate compression and serialization status).
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