(mongodb >=1.0.0)
MongoDB\Driver\ReadPreference::__construct — Construct immutable ReadPreference
$mode
[, array $tagSets
] )Creates a new ReadPreference.
mode
| Value | Description |
|---|---|
MongoDB\Driver\ReadPreference::RP_PRIMARY |
All operations read from the current replica set primary. This is the default read preference for MongoDB. |
MongoDB\Driver\ReadPreference::RP_PRIMARY_PREFERRED |
In most situations, operations read from the primary but if it is unavailable, operations read from secondary members. |
MongoDB\Driver\ReadPreference::RP_SECONDARY |
All operations read from the secondary members of the replica set. |
MongoDB\Driver\ReadPreference::RP_SECONDARY_PREFERRED |
In most situations, operations read from secondary members but if no secondary members are available, operations read from the primary. |
MongoDB\Driver\ReadPreference::RP_NEAREST |
Operations read from member of the replica set with the least network latency, irrespective of the member's type. |
tagSetsTag sets allow you to target read operations to specific members of a replica set. This parameter should be an array of associative arrays, each of which contain zero or more key/value pairs. When selecting a server for a read operation, the driver attempt to select a node having all tags in a set (i.e. the associative array of key/value pairs). If selection fails, the driver will attempt subsequent sets. An empty tag set (array()) will match any node and may be used as a fallback.
Tags are not compatible with the
MongoDB\Driver\ReadPreference::RP_PRIMARY mode and,
in general, only apply when selecting a secondary member of a set for a
read operation. However, the
MongoDB\Driver\ReadPreference::RP_NEAREST mode, when
combined with a tag set, selects the matching member with the lowest
network latency. This member may be a primary or secondary.
mode is invalid or if tagSets is provided for a primary read preference.Example #1 MongoDB\Driver\ReadPreference::__construct() example
<?php
/* Prefer a secondary node but fall back to a primary. */
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_SECONDARY_PREFERRED);
/* Prefer a node in the New York data center with lowest latency. */
$rp = new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_NEAREST, [['dc' => 'ny']]);
?>