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PHP class that resolves dog-pile effect and adds tags support for stored data
PHP
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README

MemcacheX

DESCRIPTION
MamcacheX is a PHP class based on Memcache extension. It resolves dog-pile effect and adds tags support for stored data.

It gives ability to lock records. It helps to prevent simultaneous queries to database (dog-pile effect) - while one process updates cache, another one can't do this and it waits for unlocking.
Each record in cache may have tags that helps to flush group of data associated with that tag.


INSTALLATION
Make sure that Memcache installed. Read http://ua2.php.net/manual/en/memcache.installation.php.
Include class in your code.


USAGE

Typical code you should use to invalidate all cached records with some tag.
---------------------------------------------------------------------------

$waitTime = 3000;     // Time to wait before return old data if lock setted (in milliseconds)
$waitInterval = 200;  // Interval between checking for key to unlock (in milliseconds)

$memcachex = new MemcacheX(2000, 200);
$memcachex->addServer('10.0.0.1', 11211);
$memcachex->addServer('10.0.0.2', 11211);

$tag = 'data_tag';

if ($memcachex->getTag($tag)) {
    $memcachex->deleteTag($tag);
} else {
    echo 'Tag not found';
}


Typical code you should use to resolve dog-pile effect.
-------------------------------------------------------

$waitTime = 3000;     // Time to wait before return old data if lock setted (in milliseconds)
$waitInterval = 200;  // Interval between checking for key to unlock (in milliseconds)

$memcachex = new MemcacheX(2000, 200);
$memcachex->addServer('10.0.0.1', 11211);
$memcachex->addServer('10.0.0.2', 11211);

$key = 'my_data';
$tags = array('data_tag');

$data = $memcachex->get($key);
if (false === $data) {
    if ($memcachex->lock($key) || $memcachex->isDown()) {
        // fetches data and puts it to $newData var
        // let's put $newData to cache using $key name and $tags
        $memcachex->set($key, $newData, MEMCACHE_COMPRESSED, 60, $tags);
        // you should unlock record
        $memcachex->unlock($key);
    } else {
        // another process writing data and $key already locked
        if (! $memcachex->waitForUnlock($key) || ! $data = $memcachex->get($key)) {
            // $key unlocked but has no data. You should increase lock timeout
        }
    }
}

echo $data;
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