Database / REDIS

How does Redis handle atomicity for multi-key operations?

A single Redis command, even one touching multiple keys (like MSET or SUNIONSTORE), is always atomic on its own — because command execution is single-threaded, nothing else can run in the middle of it. The harder case is atomicity across a sequence of separate commands, where Redis offers a few different tools depending on what's actually needed.

Tool	Use When
MULTI/EXEC	A fixed, known sequence of commands needs to run uninterrupted.
WATCH + MULTI/EXEC	The sequence depends on first reading a value (check-then-act), needing optimistic locking.
Lua scripting (EVAL)	Complex conditional logic across multiple keys needs to run as one atomic unit, including branching not expressible as a flat command list.

Lua scripts are the most powerful option here: the entire script executes as a single atomic step from Redis's perspective, with no other command interleaved anywhere in the middle, which lets you express logic (loops, conditionals, computed values feeding into further commands) that plain MULTI/EXEC can't, since MULTI/EXEC only queues a fixed list without letting one command's result influence the next command in the same transaction.

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Is a single command touching multiple keys, like MSET, atomic on its own? No, multi-key commands are never atomic

✗ Try again if not.

Yes, because command execution is single-threaded

✓ Correct! Well done.

Only if wrapped in MULTI/EXEC

✗ Try again if not.

What can a Lua script do that plain MULTI/EXEC cannot? Run commands across multiple keys at all

✗ Try again if not.

Nothing; they're functionally identical

✗ Try again if not.

Express conditional logic where one command's result influences the next, atomically

✓ Correct! Well done.

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Database / REDIS

How does Redis handle atomicity for multi-key operations?

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