(PECL memcache >= 0.2.0)

Memcache::addAdd an item to the server


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

Memcache::add() stores variable var with key only if such key doesn't exist at the server yet. Also you can use memcache_add() function.

Elenco dei parametri


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).

Valori restituiti

Restituisce TRUE in caso di successo, FALSE in caso di fallimento. Returns FALSE if such key already exist. For the rest Memcache::add() behaves similarly to Memcache::set().


Example #1 Memcache::add() example



/* procedural API */
memcache_add($memcache_obj'var_key''test variable'false30);

/* OO API */
$memcache_obj->add('var_key''test variable'false30);


Vedere anche:

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User Contributed Notes 5 notes

Davide Renzi
7 years ago
Race conditions happen on an heavy load server when more than one thread tries to execute memcache_add.
For example if thread A and thread B try to save the same key you can test that sometimes both return TRUE.
To have the right behaviour you can verify that the correct value is in the assigned key:

function memcache_safeadd(&$memcache_obj, $key, $value, $flag, $expire)
    if (
memcache_add($memcache_obj, $key, $value, $flag, $expire))
        return (
$value == memcache_get($memcache_obj, $key));
ktamas77 at gmail dot com
8 years ago
skeleton of a thread safe updater for an incremental counter:


= "counter";
$value = $memcache->increment($key, 1);
if (
$value === false) {
// --- read from DB ---
$query = "SELECT value FROM database";
$result = mysql_query($query);
$row = mysql_fetch_assoc($result);
$db_value = $row["value"];
$add_value = $memcache->add($key, $db_value + 1, 0, 0);
   if (
$add_value === false) {
$value = $memcache->increment($key, 1)
      if (
$value === false) {
error_log ("counter update failed.");
   } else {
$value = $db_value + 1;

// --- display counter value ---
echo $value;

vasiliy at hotger dot com
3 years ago
It looks like add() function is truly 100% atomic, and safeadd bicycle mentioned in the other comment is useless. There are few links where developers of Memcahed explained it deeper,214222
8 years ago
It's also good to note that add will succeed if the key exists but is expired
roberto at spadim,com dot br
10 years ago
if you read source code for MMC_SERIALIZED you will see at line ~1555 that [a line ~1560]

[is] serialized and that serialized values are flaged as MMC_SERIALIZED for return (fetch) code unserialize these values again
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