This change actually had a positive impact on the design of the whole
internals for clustering which is now cleaner and easier to maintain.
It is still far from perfect, but we also have to keep performances in
consideration so we can say that we ended up with a good compromise.
Previously Predis assigned an hash to each command instance which was
computed from its key, now we changed approach and the library caches
the slot assigned to each command. This works for both our client-side
sharding cluster and the upcoming redis-cluster, but the former is the
one that needed most changes.
The PredisCluster aggregate connection now only takes an instance of
StrategyInterface, which in turn wraps the chosen distributor. After
all, in order to be able to calculate the assigned slot for a command
or key, the cluster strategy must have access to the distributor that
manages the distribution of the whole keyspace. Nothing really changes
in terms of configurability as it is still possible to decide which
distributor to use for client-side sharding, it is simply different:
$distributor = new Predis\Cluster\Distribution\KetamaRing();
$strategy = new Predis\Cluster\PredisStrategy($distributor);
$cluster = new Predis\Connection\Aggregate\PredisCluster($strategy);
As for the RedisCluster aggregate connection, the only change is that
the mathematical operation of calculating the assigned slot from a key
has been completely moved inside the cluster strategy instance.
The strategy for redis-cluster does not use external distributors so
trying to StrategyInterface::getDistributor() will throw an exception.
This may change in future releases, but this is not a priority since
redis-cluster relies on a fixed, well-defined distribution mechanism.
Achieving compatibility actually required a few marginal changes:
- HHVM still has some issues with re-entrant calls to __get(). The
applied change is an hack simply because it is ugly, but it is not
wrong and does not break the signature of the options interface.
- Since we cannot rely on the PHP version to detect the availability
of socket_import_stream(), we switched to function_exists(). As an
added bonus, using function_exists() is twice faster.
- In the test suite we removed an assertion for the message of an
E_WARNING simply because HHVM emits a different message. Checking
for the warning is actually enough in that context.
While the whole test suite passes on HHVM 2.3.0, please remember that
HHVM is still in development and things could break anytime especially
in some obscure corner cases.
We now have a base test case class for Predis (namely PredisTestCase)
grouping various commonly used utility methods shared by all of the
tests in the suite, greatly improving reusability.
By raw we mean that input arguments are not filtered and responses are
not parsed, which means arguments must follow the command signature as
defined by Redis and complex responses are left untouched.
When instantiating an instance of `Predis\Command\RawCommand` you must
pass at least the command ID. You can pass further arguments in the
array or you can just set them later with `RawCommand::setArguments()`
but you cannot modify the command ID once instantiated.
$command = new Predis\Command\RawCommand(['SET', 'foo', 'bar']);
$response = $client->executeCommand($command);
While higher level abstractions built upon `Predis\Client` should just
use commands created by the profile in use, inner parts of the library
might use raw commands to provide certain functionalities making sure
that input and output of commands are always consistent, independent
of the profile.
Remi Collet
Daniele Alessandri