pipelining vs transaction in redis

Question

When we use a transaction in Redis, it basically pipelines all the commands within the transaction. And when EXEC is fired, then all the commands are executed together, thus always maintaining the atomicity of multiple commands.

Isn't this same as pipelining?

How are pipelining and transaction different? Also, why does not the single threaded nature of Redis suffice? Why do we explicitly need pipelining/transaction?

Answer 1

Pipelining is primarily a network optimization. It essentially means the client buffers up a bunch of commands and ships them to the server in one go. The commands are not guaranteed to be executed in a transaction. The benefit here is saving network round trip time for every command.

Redis is single threaded so an individual command is always atomic, but two given commands from different clients can execute in sequence, alternating between them for example.

Multi/exec, however, ensures no other clients are executing commands in between the commands in the multi/exec sequence.