# onBufferFull 当缓存区达到最高水位时触发此事件。 ```php function onBufferFull(Swoole\Server $serv, int $fd); ``` * 设置`server->buffer_high_watermark`选项来控制缓存区高水位线，单位为字节 * 触发`onBufferFull`表明此连接`$fd`的发送队列已触顶即将塞满，这时不应当再向此`$fd`发送数据 ```php $server->set([ 'buffer_high_watermark' => 8 * 1024 * 1024, ]); $server->on('onBufferFull', function ($serv, $fd) { }); ```