Memcache::add

(PECL memcache >= 0.2.0)

Memcache::add — Add an item to the server

Descrição

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.

Parâmetros

key: The key that will be associated with the item.
var: The variable to store. Strings and integers are stored as is, other types are stored serialized.
flag: Use MEMCACHE_COMPRESSED to store the item compressed (uses zlib).
expire: 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).

Valor Retornado

Retorna TRUE em caso de sucesso ou FALSE em falhas. Returns FALSE if such key already exist. For the rest Memcache::add() behaves similarly to Memcache::set().

Exemplos

Exemplo #1 Memcache::add() example


<?php

$memcache_obj = memcache_connect("localhost", 11211);

/* procedural API */
memcache_add($memcache_obj, 'var_key', 'test variable', false, 30);

/* OO API */
$memcache_obj->add('var_key', 'test variable', false, 30);

?>

Veja Também

Memcache::set() - Store data at the server
Memcache::replace() - Replace value of the existing item

Memcache::addServer

Memcache Funções

Last updated: Fri, 13 Nov 2009

add a note User Contributed Notes
Memcache::add

matt
03-Aug-2009 11:39


It's also good to note that add will succeed if the key exists but is expired

ktamas77 at gmail dot com
27-Apr-2009 09:08


skeleton of a thread safe updater for an incremental counter:



<?php



$key = "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;



?>

conrad1986 at gmail dot com
18-Feb-2009 06:47


If you want to add an entry without using the locking method below (takes up extra space), try it this way:





<?php


if(!$mc->replace("key", $data))


    $mc->set("key", $data;


?>





That way it will simply try to overwrite the value if a user has already (re)created the key. This is best in high-traffic sites where a user set()'s the data while another user has already tried a get() check and found nothing. Even this method still leaves a small microsecond window open for the same thing. However it helps prevent nasty glitches with submitting multiple entries after a get() check and the system has taken time to recompile the data to send to Memcached, after another user's request has processed this transaction.

rune(at)intermedia(dot)no
06-Oct-2008 04:04


Key may not exceed 250 chars according to memcached protocol.

php at tapirpirates dot net
03-Apr-2008 02:32


memcache has no locking mechanism, but you could implement it manually.



basic locking through the add method:



<?php

// locks time out after 5 seconds

Define( 'LOCK_TIMEOUT', 5 );



$lock = $memcache->add( 'lock:' . $key, 1, false, LOCK_TIMEOUT );

if ( $lock ) {

  // no lock on this key, so do what you want

  $value = $memcache->get( $key );

  $memcache->set( $key, $value+1 );

  // release lock

  $memcache->delete( 'lock:' . $key );

}

else {

  // variable is currently locked, so do something else

}

?>



furthermore, you could implement a loop which checks if there is a lock, and if there is, wait some time and try again, until the lock is free.



remember: locking will heavily increase your memcache hits and obviously is not what memcache is made for. altough it's not possible for a lock to be forgotten (there's a timeout after all) there is the possibility to get locked out for a very long time.



an alternative may be to implement locking through apc_add (or shared memory), but i've never tried it.



if you absolutley have to implement locks, memcached is probably the wrong solution anyway.

roberto at spadim,com dot br
18-Jun-2007 03:13


if you read source code for MMC_SERIALIZED you will see at line ~1555 that only !(is_string,is_long,is_double,is_bool) are serialized

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

add a note

Memcache::addServer

Memcache Funções

Last updated: Fri, 13 Nov 2009