framework/caching/DbCache.php
public function gc($force = false)
    {
        if ($force || mt_rand(0, 1000000) < $this->gcProbability) {
            $this->db->createCommand()
                ->delete($this->cacheTable, '[[expire]] > 0 AND [[expire]] < ' . time())
                ->execute();
        }
    }
public function gc($force = false)
    {
        if ($force || mt_rand(0, 1000000) < $this->gcProbability) {
            $this->db->createCommand()
                ->delete($this->cacheTable, '[[expire]] > 0 AND [[expire]] < ' . time())
                ->execute();
        }
    }
Removes the expired data values.
@param bool $force whether to enforce the garbage collection regardless of [[gcProbability]].
Defaults to false, meaning the actual deletion happens with the probability as specified by [[gcProbability]].