The iterators based on SCAN, SSCAN, ZSCAN and HSCAN will extend this abstract
class to share most of the logic which is common for all of the Redis commands
in the SCAN family.
This iterator allows to perform full iterations over the keyspace of a Redis
instance by wrapping the incremental nature of SCAN using an abstraction that
fits perfectly in userland code:
$client = new Predis\Client('tcp://127.0.0.1', ['profile' => '2.8']);
$iterator = new Predis\Iterator\Scan\KeyspaceIterator($client);
foreach ($iterator as $key) {
echo $key . PHP_EOL;
}
Memory consumption during an iteration is limited because elements are fetched
incrementally, on the other hand SCAN gives limited guarantees about returned
elements since the underlying collection (the keyspace in this case) can change
during the whole iteration process. The most immediate drawback is that the same
element may be returned multiple times.
See http://redis.io/commands/scan to fully understand the inner workings,
and particularly the "Scan guarantees" paragraph.
Daniele Alessandri