ADOdb

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====== Memcached Setup ======

===== Description =====
This section describes connecting to an already configured Memcache server. Information about installation and configuration of Memcached servers can be found [[https://memcached.org/|here]].

===== The Memcache Library =====
There are 2 distinct PEAR modules for connecting to a [[wp>Memcached]] server: the [[https://pecl.php.net/package/memcache|Memcache]] library and the [[https://pecl.php.net/package/memcached|Memcached]] library.
<WRAP tip>
  * Windows support is only available for the //Memcache// library.
  * //Memcache// should be used in PHP 5.x environments on UNIX platforms.
  * //Memcached// should be used in PHP 7.x environments on UNIX platforms.
  * If both libraries are available, //Memcache// will be used.
</WRAP>
===== Why can't I use the memcached library under Windows? =====
The memcached library is much more heavily featured, more modern and better maintained. The problem with it is not a problem with ADOdb, nor a problem with PHP. The PHP module is dependent on the 3rd party library **libmemcache**, which has no Windows support. Any Windows DLLs you might find floating around the web will __always__ be built on the memcache library.


===== Usage =====
<code php>

$db = NewADOConnection($driver='mysqli');

/*
 * Enable memcache
 */
$db->memCache = true;

/*
 * Add one or more servers, for use in distributed systems
 */
$db->memCacheHost = array('192.168.0.78', '192.168.0.79', '192.168.0.80');

/*
 * Optionally add the server port if it differs from the default
 */
$db->memCachePort = 11211;

/*
 * Use 'true' to store the item compressed (uses zlib)
 */
$db->memCacheCompress = false;

/*
 * We connect to the database, not the memcache server
 */
$db->Connect('localhost','mysql-user','mysql-password','employees');

/*
 * look for a cached query with a life of 2400 seconds
 */
$sql = 'SELECT code,description FROM xref_table';
$db->cacheExecute(2400,$sql);

</code>
===== Adding Weighted Server Groups =====

From ADOdb version 5.22, the **memcached** library supports the use of **//Weighted server groups//**, in which a specific server can be forced to return a result a specific percentage of the time. 

If the feature is used, the total weighting of the server group must equal 100%.  To achieve this, the configuration of the servers must be defined in a different way to the default. Each host is defined as an array:

<code php>
array(
 'host'=> The host name,
 'port'=> The port, defaults to 11211,
 'weight'=> A percentage, up to 100,
);
</code>

The host arrays are then combined together. In this example 86.91 serves 70% of requests and 86.92 serves 30%
<code php>

$hosts = array(
    array('host'=>'192.168.86.91','port'=>'11211','weight'=>70),
    array('host'=>'192.168.86.92','port'=>'11211','weight'=>30),
    );

$db = NewADOConnection($driver='mysqli');

/*
 * Enable memcache
 */
$db->memCache = true;

/*
 * Add the weighted servers in $memCacheHosts. All other parameters are ignored.
 */
$db->memCacheHost = $hosts
 
</code>

===== Adding options to the memcached server =====
From ADOdb version 5.22, [[https://www.php.net/manual/en/memcached.setoption.php|server options]] can be set on the **Memcached** connection by use of the **memCacheOptions** array

<code php>

$hosts = array(
    array('host'=>'192.168.86.91','port'=>'11211','weight'=>70)
    array('host'=>'192.168.86.92','port'=>'11211','weight'=>30)
    );

$db = NewADOConnection($driver='mysqli');

/*
 * Enable memcache
 */
$db->memCache = true;

/*
 * Add the weighted servers in $memCacheHosts
 */
$db->memCacheHost = $hosts;

/*
* Set some options
*/
$db->memCacheOptions = array(Memcached::OPT_HASH=>Memcached::HASH_MURMUR);
</code>

===== Using Debug Mode  =====

The size of query results that can be cached by the memcached server is limited by server configuration. The default is quite small. If the query is too large, and [[v5:userguide:debug|debugging]] is enabled, then an error is displayed.

<code>
3849805e4e026b9e7c485999a24a95c6 cache failure: Item with such key doesn't exists on the memcached server.
(this is a notice and not an error)
-----<hr>

(mysqli): SELECT * FROM employees

------<hr>

Notice: MemcachePool::set(): Server 192.168.0.78 (tcp 11211, udp 0) failed with:
SERVER_ERROR object too large for cache
(3) in C:\dev\github\mssqlnative-fixes\adodb-memcache.lib.inc.php on line 94
Failed to save data at the memcached server!

Cache write error

PHP Notice:  MemcachePool::set(): Server 192.168.0.78 (tcp 11211, udp 0) failed with:
SERVER_ERROR object too large for cache (3)
in C:\dev\github\mssqlnative-fixes\adodb-memcache.lib.inc.php on line 94
</code>

ADOdb currently has no mechanism for splitting large queries into smaller chunks.


{{tag>[memcached cache]}}