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<?php
/* FileCache
* ---
* Saves serialized data into filesystem.
* Use it for expensive database-queries.
* Performanve on a NVMe-SSD drive is really great;
* (even better than MemCached and Redis)
* performance on a typical HDD is just fair.
*
* NOTE:
* Memcached and Redis are much faster cache-technologies
* and generally recommended; but they are not always available;
* FileCache is (almost) always available;
*
* Before tou decide on your caching technology
* run some benchmarks.
*/
class FileCache implements Cache_interface
{
/** store
* ---
* serializes and saves data in a file
* along with TTL (time-to-live)
*/
public function set(string $key, $data, int $ttl)
{
// filename is a hashed 48-hex-digit string
// probability of collision = exp( (-k*(k-1)) / 2N )
// ex: for 10tril.samples P(collision) = 1.5E-11%
$filename = FILECACHE_PATH . sha1($key);
// Opening file for write
$h = fopen($filename, 'w');
if (!$h) throw new Exception('Can not write to cache');
// Serialize along with the TTL
$data = serialize( array(
time() + $ttl, // array[0] holds expiration time
$data) // array[1] holds the actual data
);
if (fwrite($h,$data) === false) {
throw new Exception('Can not write to cache');
}
fclose($h);
}
/** fetch
* ---
* feth data for certain key
* @param $key (string)
* @return fetched $data -or- false on failure
*/
public function get(string $key)
{
$filename = FILECACHE_PATH . sha1($key);
// can not read the cache-file? return false
if (!file_exists($filename) || !is_readable($filename)) return false;
$data = file_get_contents($filename); // get cache-file contents
$data = @unserialize($data); // unserialize
if (!$data) {
// Unlinking the file when unserializing failed
unlink($filename);
return false;
}
// checking if the data was expired
if (time() > $data[0]) {
// Unlinking
unlink($filename);
return false;
}
return $data[1];
}
public function flush(int $olderThan = 0)
{
return false; // reply false until implementation
}
}
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