Redis transactions allow you to execute a series of commands in a single, atomic operation. This ensures that either all commands are executed or none are, maintaining data integrity. Transactions in Redis are handled using the MULTI, EXEC, DISCARD, and WATCH commands.

1. Atomicity: All commands in a transaction are executed as a single unit.
2. Isolation: Commands in a transaction are not visible to other clients until the transaction is executed.
3. Consistency: Ensures that the database remains in a consistent state before and after the transaction.

• MULTI: Marks the start of a transaction block.
• EXEC: Executes all commands issued after MULTI.
• DISCARD: Cancels the transaction, discarding all commands issued after MULTI.
• WATCH: Monitors one or more keys to determine if the transaction should be aborted.

In this example:

1. MULTI starts the transaction.
2. SET key1 "value1" and SET key2 "value2" are queued.
3. EXEC executes both commands atomically.

1. MULTI: When you issue the MULTI command, Redis enters a transactional state. All subsequent commands are queued instead of being executed immediately.
2. EXEC: When you issue the EXEC command, all queued commands are executed in the order they were queued. If any command fails, none of the commands are executed.
3. DISCARD: If you decide to cancel the transaction, you can issue the DISCARD command, which will clear the queue of commands.
4. WATCH: The WATCH command is used for optimistic locking. It monitors the specified keys and if any of them are modified before the transaction is executed, the transaction is aborted.

In this example:

1. WATCH key1 monitors key1 for changes.
2. MULTI starts the transaction.
3. SET key1 "new_value" and SET key2 "another_value" are queued.
4. EXEC attempts to execute the transaction. If key1 was modified after the WATCH command, the transaction is aborted.

Exercise 1: Basic Transaction

1. Start a transaction.
2. Set the key user:1000 to the value John Doe.
3. Set the key user:1001 to the value Jane Doe.
4. Execute the transaction.

Solution:

Exercise 2: Using WATCH

1. Watch the key balance.
2. Start a transaction.
3. Increment the key balance by 100.
4. Execute the transaction.

Solution:

• Forgetting to EXEC: If you forget to issue the EXEC command, the transaction will not be executed.
• Using WATCH incorrectly: Ensure that you issue the WATCH command before starting the transaction with MULTI.
• Handling transaction failures: Always check the result of EXEC to handle cases where the transaction was aborted.

In this section, you learned about Redis transactions, including the key commands MULTI, EXEC, DISCARD, and WATCH. You also practiced creating basic transactions and using optimistic locking with WATCH. Understanding transactions is crucial for maintaining data integrity and consistency in your Redis applications. In the next section, we will explore pipelining to optimize the performance of multiple Redis commands.