Using gethostbyname, we will reuse the same (first) IP address for
each request. Here, we choose the IP we use randomly.
This is practical in a case where we have multiple redis read-only
slaves that can't invidually support the full application load, but are
accessible through a single hostname.
Providing a basic hint in the exception message about the server that caused
a connection exception could be useful especially with aggregated connections.
This is in response to issue #110.
This cannot be implemented for previous versions of PHP because we
need socket_import_stream() to extract the underlying socket resource
from the stream in order to be able to set the TCP_NODELAY flag.
This commit reflects the recent change from the redis unstable branch
in which the number of hash slots was increased from 4096 to 16384.
See https://github.com/antirez/redis/commit/ebd666d for reference.
This class works just like Predis\Connection\PhpiredisConnection but
it does not require the socket extensions since it relies on PHP's
native streams thus allowing the use of persistent connections.
We should actually make use of more protected methods in this
class instead of the private ones, this is most likely going
to be addressed in future commits.
See also issue #86 on GitHub for the reason behind this change.
Connection classes should just handle, convert and return simple Redis
types while parsing and transforming structured replies should be done
by consumers (see Predis\Client or Predis\Transaction\MultiExecContext).
This actually makes more sense considering that parsing a complex response
with the associated command parser may require different actions. As an
example, the result of EXEC is a multibulk that holds the actual responses,
so we really need to parse each one of its elements and we should also
make sure that iterable multibulks are consumed. We already did that
previously, but it was weird knowing that command parsers were applied
by the connection class.
This also moves some duplicated logic away from each connection class
implementation which is a nice bonus.
When no server profile is specified, the connection factory will not push
any initialization command to the newly created connection object.
This change is mainly useful when using redis-cluster and also makes it
possible to easily inject commands such as "SCRIPT LOAD" at initialization
time by grouping everything into one common place simply by extending the
connection factory class.
We extract the keys from commands using the second argument of EVAL /
EVALSHA which specifies the number of arguments that must be treated
as keys (used to populate the KEYS table in the Lua script) and then
we check if there is only one key since redis-cluster right now does
not support multi-keys requests.
Our scripted command abstraction is also supported.
This should make things a tiny bit faster (we are speaking about micro
optimizations anyway) but more importantly it results in a better
encapsulation.
This makes it possible to easily assign a connection to a slot range
using the key "slots" in connection parameters like in the following
example:
$parameters = array(
'tcp://127.0.0.1:6379?slots=0-1364',
'tcp://127.0.0.1:6380?slots=1365-2729',
'tcp://127.0.0.1:6381?slots=2730-4095',
);
$options = array('cluster' => 'redis');
$client = new Predis\Client($parameters, $options);
It is possible to get the full list of slot ranges for each node of
the cluster using redis-cli connected to one of the nodes:
./redis-cli -h 127.0.0.1 -p 6379 CLUSTER NODES
The last column in the resulting output contains the slots assigned
to each instance participating to the redis cluster.
This is useful to avoid guessing the correct server instance at runtime
thus reducing the overhead of a guess-and-try approach since relying on
-ASK or -MOVED responses returned by a node is a costly operation.
For now, you can pre-associate slots using the "cluster" client option:
$parameters = array(
'tcp://127.0.0.1:6379',
'tcp://127.0.0.1:6380',
'tcp://127.0.0.1:6381',
);
$options = array(
'cluster' => function ($options) {
$cluster = new Predis\Connection\RedisCluster();
$cluster->setSlots(0, 1364, '127.0.0.1:6379');
$cluster->setSlots(1365, 2729, '127.0.0.1:6380');
$cluster->setSlots(2730, 4095, '127.0.0.1:6381');
return $cluster;
},
);
$client = new Predis\Client($parameters, $options);
In the future we will make the slots configuration easier by fetching
the configuration from a node using the command "CLUSTER NODES" or by
pre-computing the slices of slots associated to a node when adding it
to the cluster connection object.
This is needed because redis-cluster does not support the same commands
or operations that can be performed with our client-side managed predis
cluster.
For example redis-cluster does not support key tagging (that is, parts
of a key enclosed by {...} to hash only that specific part of a key)
and multiple-key operations suchs as MGET, MSET, SDIFF, SUNION or SINTER.
Some multiple-key operations can be performed anyway if the command has
only one key (e.g. "MGET foo" and "MSET foo bar" will not fail).
This implementation is capable of handling "ASK" and "MOVED" replies
returned by Redis when one of the nodes asks the client for temporary
or permanent redirects of a slot to a different node.
Performances look almost on par with our client-side sharding solution
and everything looks already relatively stable.
Tests are still missing.
The reason for this change is to support the upcoming redis-cluster since
it has different behaviors compared to the client-side cluster implementation
provided by Predis. For example redis-cluster will not support key tags or
certain operations currently available with our client-side implementation.
Alexandru Patranescu
Thomas Orozco
Daniele Alessandri