Transaction execution model in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a transaction in Redis?

A transaction in Redis is a group of commands executed as a single, atomic operation, ensuring all commands run sequentially without interruption.

beginner

What Redis command starts a transaction?

The MULTI command starts a transaction in Redis, queuing subsequent commands for atomic execution.

intermediate

How does Redis ensure commands in a transaction are executed atomically?

Redis queues commands after MULTI and executes them all at once with EXEC, preventing other clients from running commands in between.

intermediate

What happens if a command inside a Redis transaction fails before EXEC?

Commands are only queued after MULTI; errors in commands are reported only when EXEC runs. If a command is invalid, EXEC still runs all queued commands including the invalid one, but returns an error for that command.

advanced

What is the role of the WATCH command in Redis transactions?

WATCH monitors keys for changes. If any watched key changes before EXEC, the transaction aborts to avoid conflicts.

Which command starts a Redis transaction?

A EXEC

B MULTI

C WATCH

D BEGIN

The MULTI command starts a transaction by queuing commands.

What does the EXEC command do in Redis?

A Executes all queued commands atomically

B Starts a transaction

C Cancels the transaction

D Monitors keys for changes

EXEC runs all commands queued after MULTI atomically.

If a watched key changes before EXEC, what happens?

A The key is deleted

B Transaction executes normally

C Redis throws an error immediately

D Transaction aborts

The transaction aborts to avoid conflicts if a watched key changes.

Can Redis transactions rollback partially if a command fails?

A No partial rollback; commands run atomically but errors are reported after execution

B No, all commands run or none run

C Yes, only failed commands are skipped

D Yes, it rolls back all commands

Redis executes all queued commands atomically; errors are reported after execution but no partial rollback occurs.

What is the purpose of the DISCARD command in Redis?

A Execute queued commands

B Start watching keys

C Cancel the transaction and clear queued commands

D Commit changes permanently

DISCARD cancels the transaction and clears all queued commands.

Explain how Redis transactions ensure atomic execution of multiple commands.

Think about how commands are queued and then executed together.

Describe the role of the WATCH command in Redis transactions and how it helps avoid conflicts.

Consider how Redis detects changes to keys before committing a transaction.