(PECL mongo >=1.6.0)
MongoCursorInterface::setReadPreference — Set the read preference for this query
$read_preference
[, array $tags
] )read_preferenceThe read preference mode: MongoClient::RP_PRIMARY, MongoClient::RP_PRIMARY_PREFERRED, MongoClient::RP_SECONDARY, MongoClient::RP_SECONDARY_PREFERRED, or MongoClient::RP_NEAREST.
tagsAn array of zero or more tag sets, where each tag set is itself an array of criteria used to match tags on replica set members.
Returns this cursor.
Emits E_WARNING if either parameter is invalid, or if one or more tag sets are provided with the MongoClient::RP_PRIMARY read preference mode.