PINGPing the server; returns PONG or echoes the optional message.
| 语法 | PING [message] |
| 分组 | connection |
| 参数个数 | -1 |
| 起始版本 | 1.0.0 |
| 标志 | readonly |
| 复杂度 | O(1) |
| Redis 兼容性 | differs: kevy has no RESP2 subscriber mode, so PING while subscribed does not switch to the array form and non-pubsub commands stay legal on a subscribed connection |