Returns the latency of this server in milliseconds

# MongoDB\Driver\Server::getLatency

(mongodb >=1.0.0)

MongoDB\Driver\Server::getLatency — Returns the latency of this server in milliseconds

### 说明

final public function MongoDB\Driver\Server::getLatency(): ?integer

Returns the latency of this server in milliseconds. This is the client's measured » round trip time of a `hello` command.

### 参数

此函数没有参数。

### 返回值

Returns the latency of this server in milliseconds, or `null` if no latency has been measured (e.g. client is connected to a load balancer).

### 错误／异常

- Throws MongoDB\Driver\Exception\InvalidArgumentException on argument parsing errors.

### 更新日志

版本 | 说明
--- | ---
PECL mongodb 1.11.0 | This method will return `null` if no latency has been measured. In earlier versions, an integer was always returned and an unset value might be reported as `-1`.

### 示例

示例 #1 MongoDB\Driver\Server::getLatency() example

    <?php

    $manager = new MongoDB\Driver\Manager("mongodb://localhost:27017/");
    $server = $manager->selectServer();

    var_dump($server->getLatency());

    ?>

以上示例的输出类似于：

    int(592)

### 参见

- MongoDB\Driver\Server::getInfo() - Returns an array of information describing this server
- MongoDB\Driver\ServerDescription::getRoundTripTime() - Returns the server's round trip time in milliseconds
- » Server Discovery and Monitoring Specification

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