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antirez authored
Sometimes it can be useful for clients to completely disable replies from the Redis server. For example when the client sends fire and forget commands or performs a mass loading of data, or in caching contexts where new data is streamed constantly. In such contexts to use server time and bandwidth in order to send back replies to clients, which are going to be ignored, is a shame. Multiple mechanisms are possible to implement such a feature. For example it could be a feature of MULTI/EXEC, or a command prefix such as "NOREPLY SADD myset foo", or a different mechanism that allows to switch on/off requests using the CLIENT command. The MULTI/EXEC approach has the problem that transactions are not strictly part of the no-reply semantics, and if we want to insert a lot of data in a bulk way, creating a huge MULTI/EXEC transaction in the server memory is bad. The prefix is the best in this specific use case since it does not allow desynchronizations, and is pretty clear semantically. However Redis internals and client libraries are not prepared to handle this currently. So the implementation uses the CLIENT command, providing a new REPLY subcommand with three options: CLIENT REPLY OFF disables the replies, and does not reply itself. CLIENT REPLY ON re-enables the replies, replying +OK. CLIENT REPLY SKIP only discards the reply of the next command, and like OFF does not reply anything itself. The reason to add the SKIP command is that it allows to have an easy way to send conceptually "single" commands that don't need a reply as the sum of two pipelined commands: CLIENT REPLY SKIP SET key value Note that CLIENT REPLY ON replies with +OK so it should be used when sending multiple commands that don't need a reply. However since it replies with +OK the client can check that the connection is still active and all the previous commands were received. This is currently just into Redis "unstable" so the proposal can be modified or abandoned based on users inputs.
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