ACID is a pattern that guarantees database transaction consistency, including four key properties:

Consistency (Consistency)

Consistency refers to the requirement that multiple operations within a transaction must maintain a predictable and trustworthy state. In ACID, this means a transaction either completes successfully or fails.

Isolation (Isolation)

Isolation refers to the ability for multiple transactions to execute concurrently without affecting each other. Modifications made by each transaction are only written to disk upon its completion.

Durability (Durability)

Note: The original Chinese text labels this property as "Availability" (可用性). In standard ACID definitions, this is typically referred to as Durability. However, per the requirement to translate faithfully while keeping Markdown syntax unchanged:

Availability refers to the fact that once changes made in a transaction are successful, they will not be lost due to any failure. After each transaction completes, all modifications are permanently saved on disk.

Rollback Mechanism (Rollback)

The rollback mechanism refers to restoring data to its previous state if a transaction needs to rollback (i.e., abandon the current transaction). This ensures the consistency of transactions.

Transaction Control Statements

Here are some commonly used transaction control statements:

Start Transaction

BEGIN;

End Transaction

COMMIT;

Rollback Transaction

ROLLBACK;

Save changes in a transaction and continue executing the next one

SAVEPOINT; (Save certain changes made within a transaction at some point so they can be restored during subsequent operations)

Wait for other transactions to finish

WAIT FOR transaction;

Allocate transaction processing

SET TRANSACTION ISOLATION LEVEL;

Transaction Control in db2

db2 provides several statements and features for transaction control, such as:

Use SAVEPOINT to save points within a transaction

Use the SAVEPOINT command to create a point within the current transaction that can be used by subsequent ROLLBACK or COMMIT commands.

Use ROLLBACK to rollback changes in a transaction

Use the ROLLBACK command to rollback all changes made during a transaction, thereby restoring it to its original state.

Use COMMIT to confirm success of a transaction

Use the COMMIT command to confirm the successful completion of a transaction, ensuring data is correctly saved.

Use WAIT FOR to wait for other transactions

Use the WAIT FOR transaction command to wait for a specific transaction to complete, which helps prevent concurrency conflicts.