(PECL mongo >=1.1.0)
Mongo::switchSlave — Choose a new slave for slaveOkay reads
This choses a random slave for a connection to read from. It is called automatically by the driver and should not need to be used. It calls Mongo::getHosts() (to refresh the status of hosts) and Mongo::getSlave() (to get the return value).
See the query section of this manual for information on distributing reads to slaves.
此函数没有参数。
The address of the slave this connection is using for reads. This may be the same as the previous address as addresses are randomly chosen. It may return only one address if only one secondary (or only the primary) is available.
For example, if we had a three member replica set with a primary, secondary, and arbiter this method would always return the address of the secondary. If the secondary became unavailable, this method would always return the address of the primary. If the primary also became unavailable, this method would throw an exception, as an arbiter cannot handle reads.
Throws a MongoException (error code 15) if it is called on a non-replica-set connection. It will also throw MongoExceptions if it cannot find anyone (primary or secondary) to read from (error code 16).