Time complexity: O(1)
PONG if no argument is provided, otherwise return a copy of the
argument as a bulk.
This command is useful for:
- Testing whether a connection is still alive.
- Verifying the server's ability to serve data - an error is returned when this isn't the case (e.g., during load from persistence or accessing a stale replica).
- Measuring latency.
If the client is subscribed to a channel or a pattern, it will instead return a multi-bulk with a "pong" in the first position and an empty bulk in the second position, unless an argument is provided in which case it returns a copy of the argument.
Simple string reply, and specifically
PONG, when no argument is provided.
Bulk string reply the argument provided, when applicable.
dragonfly> PING "hello world"