(mongodb >=1.0.0)
MongoDB\Driver\ReadPreference::__construct — Create a new ReadPreference
$mode
, array $tagSets = null
, array $options = array()
)Constructs a new MongoDB\Driver\ReadPreference, which is an immutable value object.
mode
| Value | Description |
|---|---|
MongoDB\Driver\ReadPreference::RP_PRIMARY or "primary" |
All operations read from the current replica set primary. This is the default read preference for MongoDB. |
MongoDB\Driver\ReadPreference::RP_PRIMARY_PREFERRED or "primaryPreferred" |
In most situations, operations read from the primary but if it is unavailable, operations read from secondary members. |
MongoDB\Driver\ReadPreference::RP_SECONDARY or "secondary" |
All operations read from the secondary members of the replica set. |
MongoDB\Driver\ReadPreference::RP_SECONDARY_PREFERRED or "secondaryPreferred" |
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 or "nearest" |
Operations read from member of the replica set with the least network latency, irrespective of the member's type. |
tagSets
Tag 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.
options
| Option | Type | Description |
|---|---|---|
| hedge | object|array |
Specifies whether to use » hedged reads, which are supported by MongoDB 4.4+ for sharded queries.
Server hedged reads are available for all non-primary read preferences
and are enabled by default when using the |
| maxStalenessSeconds | int |
Specifies a maximum replication lag, or "staleness", for reads from secondaries. When a secondary's estimated staleness exceeds this value, the driver stops using it for read operations.
If specified, the max staleness must be a signed 32-bit integer
greater than or equal to
Defaults to
This option is not compatible with the
|
mode is invalid.tagSets is provided for a primary read preference or is malformed (i.e. not an array of zero or more documents)."maxStalenessSeconds" option is provided for a primary read preference or is out of range.
| 版本 | 说明 |
|---|---|
| PECL mongodb 1.8.0 |
Added the "hedge" option.
|
| PECL mongodb 1.3.0 |
The |
| PECL mongodb 1.2.0 |
Added a third |
Example #1 MongoDB\Driver\ReadPreference::__construct() example
<?php
/* Prefer a secondary node but fall back to a primary. */
var_dump(new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_SECONDARY_PREFERRED));
/* Prefer a node in the New York data center with lowest latency. */
var_dump(new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_NEAREST, [['dc' => 'ny']]));
/* Require a secondary node whose replication lag is within two minutes of the primary */
var_dump(new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_SECONDARY, null, ['maxStalenessSeconds' => 120]));
/* Explicitly enable server hedged reads */
var_dump(new MongoDB\Driver\ReadPreference(MongoDB\Driver\ReadPreference::RP_SECONDARY, null, ['hedge' => ['enabled' => true]]));
?>
以上例程会输出：
object(MongoDB\Driver\ReadPreference)#1 (1) {
["mode"]=>
string(18) "secondaryPreferred"
}
object(MongoDB\Driver\ReadPreference)#1 (2) {
["mode"]=>
string(7) "nearest"
["tags"]=>
array(1) {
[0]=>
object(stdClass)#2 (1) {
["dc"]=>
string(2) "ny"
}
}
}
object(MongoDB\Driver\ReadPreference)#1 (2) {
["mode"]=>
string(9) "secondary"
["maxStalenessSeconds"]=>
int(120)
}
object(MongoDB\Driver\ReadPreference)#1 (2) {
["mode"]=>
string(9) "secondary"
["hedge"]=>
object(stdClass)#1 (1) {
["enabled"]=>
bool(true)
}
}