This change does not affect distribution but simply separates the two
concepts of connection ID (ip:port pair) and alias (value set via the
"alias" connection parameter), the method getConnectionByAlias() has
been added to reflect this change.
The method getConnectionBySlot() has also been added.
This method improves the previous one, which worked only by picking a
connection by ID, allowing users to specify a selector type among the
following ones: "id", "key", "slot", "command". These selectors are
expanded internally to methods, invoked against the connection object
in use by the client, that follow the getConnectionByXXX() convention
already in use through the library:
id => getConnectionById()
key => getConnectionByKey()
slot => getConnectionBySlot()
command => getConnectionByCommand()
The underlying connection does not necessarily need to implement the
aggregate connection interface as the client relies on a duck-typing
approach by using method_exists().
This new method acts exactly like "getClientFor()" by returning a new
client instance for the specified node unless a callback is passed as
the second argument, in this case the callback is invoked and the new
client instance is passed to it. The value returned by the callback
is used as the return value of the "on()" method.
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.
* Renamed SingleConnectionInterface to NodeConnectionInterface since
this name is better and makes even more sense in the context of
cluster and replication scenarios.
* Moved specialized aggregate connections (the ones implementing both
predis and redis cluster and master/slave replication) in a newly
created Predis\Connection\Aggregate sub-namespace.
* Removed the "Connection" part from names of aggregate connection
interfaces in the Predis\Connection\Aggregate sub-namespace.
* Changed "Composable" to "Composite" in the name of interfaces and
classes that can use pluggable protocol processors.
Till Krüss
Till Krüss
Fran Moreno
Daniele Alessandri