Replica Sets
Replica Sets
Replica Sets
To connect to a replica set, specify one or more
members of the set and use the “replicaSet” option.
Multiple servers may be delimited by a comma.
Example #1 ReplicaSet seed list
<?php
// Using multiple servers as the seed list (prefered)
$m = new MongoClient("mongodb://rs1.example.com:27017,rs2.example.com:27017/?replicaSet=myReplSetName");
// Using one server as the seed list
$m = new MongoClient("mongodb://rs1.example.com:27017", array("replicaSet" => "myReplSetName"));
// Using multiple servers as the seed list
$m = new MongoClient("mongodb://rs1.example.com:27017,rs2.example.com:27017", array("replicaSet" => "myReplSetName"));
?>The PHP driver will query the database server(s)
listed to determine the primary. So long as it can connect to at
least one host listed and find a primary, the connection will
succeed. If it cannot make a connection to any servers listed or
cannot find a primary, a MongoConnectionException will be thrown.
You should always provide a seed list with more
than one member of the ReplicaSet. For highest availability you
should seed with at least one server from each of your
datacenters.
The host names that you specify in the seed list
must match the host names in the replica
set configuration. This is because the driver only uses the host
names in the replica set configuration to create the hash for its
persistent connections.
For example, if an IP address is used in the seed
list and the replica set is configured with host names, the driver
will discard any seed list connection(s) that differ from the
canonical host names reported by the replica set. Effectively,
these non-canonical seed list connections will be recreated on each
request, greatly reducing the benefit of using persistent
connections.
The driver does not
support connecting to different replica sets with the same name.
This extends beyond one script so make sure to have separate names
for each of your replica sets. That also means that you can
not do this:
Example #2 Wrong replica set name
duplication
<?php
$m = new MongoClient("mongodb://devserver1,devserver2,devserver3/?replicaSet=repset");
$m = new MongoClient("mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=repset");
?>Instead, you need to have two different names for
your replica sets:
Example #3 Correct use of two replica set
names
<?php
$m = new MongoClient("mongodb://devserver1,devserver2,devserver3/?replicaSet=devset");
$m = new MongoClient("mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=prodset");
?>If the primary becomes unavailable, an election
will take place and a secondary will be promoted to the role of
primary (unless a majority vote cannot be established). During this
time (» 20-60 seconds), the
connection will not be able to perform any write operations and
attempts to do so will result in an exception. Connections to
secondaries will still be able to perform reads.
Note:
The default Read Preference is to only read from the primary.
During the election process there is no primary, and all read will
therefore fail.It is recommended to use
MongoClient::RP_PRIMARY_PREFERRED
Read Preference for applications that require high availability for
reads, as reads will only be executed on the secondaries when there
simply isn’t a primary available.
Once a primary is elected, attempting to perform a
read or write will allow the driver to detect the new primary. The
driver will make this its primary database connection and continue
operating normally.
The health and state of a secondary is checked
every 5 seconds (configurable with mongo.ping_interval) or when the next operation occurs
after 5 seconds. It will also recheck the configuration when the
driver has a problem reaching a server.
Replica set failovers are checked every 60 seconds
(configurable with mongo.is_master_interval), and whenever a write
operation fails when using acknowledged writes.
Secondaries may be behind the primary in
operations, so your application must be able to handle out-of-date
data when using Read Preferences other then
MongoClient::RP_PRIMARY.
For more information on replica sets, see the
» core documentation.
See Also
Changelog
| Version | Description |
|---|---|
| 1.0.9 | Added support for connecting to ReplicaSet and automatic failover. |