Transaction states in DBMS Theory - Step-by-Step Execution

Concept Flow - Transaction states

Start Transaction

↓

Active State

↓

Decision: Commit or Rollback?

↓

Partially Committed

↓

Committed

↓

End Transaction

A transaction starts active, then either commits or aborts, passing through intermediate states before ending.

Execution Sample

DBMS Theory

BEGIN TRANSACTION;
-- perform operations
COMMIT;

Starts a transaction, performs operations, then commits to save changes.

Analysis Table

Step	Transaction State	Action	Result
1	Start	Begin transaction	Transaction is active
2	Active	Perform operations	Operations executed
3	Active	Decide to commit	Move to partially committed
4	Partially Committed	Commit changes	Changes saved, move to committed
5	Committed	End transaction	Transaction ends successfully

💡 Transaction ends after commit; all changes are saved permanently.

State Tracker

Transaction State	Start	After Step 2	After Step 3	After Step 4	Final
State	Start	Active	Partially Committed	Committed	End

Key Insights - 2 Insights

Why is there a 'Partially Committed' state before 'Committed'?

The 'Partially Committed' state means all operations are done but changes are not yet permanent; this is shown in execution_table step 3 and 4.

What happens if a failure occurs during the 'Active' state?

If failure occurs, the transaction moves to 'Failed' then 'Aborted' state, rolling back changes, which is not shown here but is a common alternate path.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the transaction state?

A Partially Committed

B Committed

C Active

D Failed

💡 Hint

Refer to the 'Transaction State' column at step 3 in execution_table.

At which step does the transaction end successfully?

A Step 5

B Step 2

C Step 3

D Step 4

💡 Hint

Check the 'Result' column for when the transaction ends in execution_table.

If the transaction fails during operations, which state would it enter next?

A Committed

B Aborted

C Partially Committed

D Active

💡 Hint

Recall the concept_flow shows failure leads to 'Aborted' state.

Concept Snapshot

Transaction states flow from Start -> Active -> (Commit or Rollback) -> End.
Active means operations are running.
Partially Committed means operations done but not saved.
Committed means changes saved permanently.
Failed and Aborted mean rollback due to error.
Transaction ends after commit or abort.

Full Transcript

A transaction in a database management system goes through several states. It starts with the 'Start' state when the transaction begins. Then it moves to 'Active' while operations are performed. After operations, if the transaction is successful, it moves to 'Partially Committed' where all operations are done but changes are not yet permanent. Then it moves to 'Committed' where changes are saved permanently. Finally, the transaction ends successfully. If an error occurs during 'Active', the transaction moves to 'Failed' and then 'Aborted', rolling back changes and ending the transaction without saving. This flow ensures data integrity and consistency.

Practice

1. Which of the following is NOT a valid state of a database transaction?

easy

A. Running

B. Waiting

C. Committed

D. Failed

Solution

1. Step 1: List common transaction states

   Common transaction states include Running (active), Waiting (blocked), Committed (successfully completed), and Aborted (rolled back).

2. Step 2: Identify invalid state

   "Failed" is not a standard transaction state; instead, "Aborted" or "Rolled back" is used for unsuccessful transactions.

3. Final Answer:

   Failed -> Option D

4. Quick Check:

   Standard states exclude "Failed" [OK]

Hint: Remember standard states: Running, Waiting, Committed, Aborted [OK]

Common Mistakes:

• Confusing 'Failed' with 'Aborted'
• Thinking 'Waiting' is not a state
• Assuming 'Failed' is official terminology

2. Which SQL command is used to move a transaction from the 'Running' state to the 'Committed' state?

easy

A. ROLLBACK

B. COMMIT

C. SAVEPOINT

D. BEGIN

Solution

1. Step 1: Understand transaction commands

   ROLLBACK undoes changes, SAVEPOINT sets a restore point, BEGIN starts a transaction, and COMMIT finalizes changes.

2. Step 2: Identify command to commit

   COMMIT is the command that moves a transaction from Running (active) to Committed (completed) state.

3. Final Answer:

   COMMIT -> Option B

4. Quick Check:

   COMMIT finalizes transaction [OK]

Hint: COMMIT saves changes permanently, ROLLBACK cancels [OK]

Common Mistakes:

• Confusing ROLLBACK with COMMIT
• Using SAVEPOINT to commit
• Thinking BEGIN commits

3. Consider the following sequence of SQL commands in a transaction:

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

What is the final state of this transaction after execution?

medium

A. Committed

B. Aborted

C. Running

D. Waiting

Solution

1. Step 1: Analyze the transaction commands

   The transaction starts with BEGIN, performs two updates, then ends with COMMIT.

2. Step 2: Determine transaction state after COMMIT

   COMMIT finalizes the transaction successfully, so the state becomes Committed.

3. Final Answer:

   Committed -> Option A

4. Quick Check:

   COMMIT means transaction is Committed [OK]

Hint: COMMIT means transaction completed successfully [OK]

Common Mistakes:

• Thinking transaction remains Running after COMMIT
• Confusing Aborted with Committed
• Assuming Waiting state after COMMIT

4. Identify the error in this transaction sequence:

BEGIN;
UPDATE inventory SET quantity = quantity - 5 WHERE product_id = 10;
ROLLBACK;
COMMIT;

medium

A. COMMIT after ROLLBACK is invalid

B. ROLLBACK should come after COMMIT

C. BEGIN is missing

D. No error, sequence is correct

Solution

1. Step 1: Understand ROLLBACK and COMMIT order

   ROLLBACK cancels the transaction, so no changes remain to commit afterwards.

2. Step 2: Identify invalid command sequence

   After ROLLBACK, issuing COMMIT is invalid because the transaction is already aborted.

3. Final Answer:

   COMMIT after ROLLBACK is invalid -> Option A

4. Quick Check:

   Cannot COMMIT after ROLLBACK [OK]

Hint: ROLLBACK cancels; no COMMIT allowed after rollback [OK]

Common Mistakes:

• Thinking COMMIT can follow ROLLBACK
• Assuming ROLLBACK should come after COMMIT
• Missing BEGIN statement

5. A transaction is in the 'Waiting' state because it is blocked by another transaction holding a lock. Which of the following actions will NOT help the waiting transaction to proceed?

hard

A. The blocking transaction commits

B. The blocking transaction rolls back

C. The waiting transaction issues a COMMIT

D. The blocking transaction releases the lock

Solution

1. Step 1: Understand 'Waiting' state cause

   Waiting occurs when a transaction is blocked due to locks held by another transaction.

2. Step 2: Analyze actions that unblock waiting

   If the blocking transaction commits, rolls back, or releases the lock, the waiting transaction can proceed.

3. Step 3: Identify action that does NOT help

   The waiting transaction issuing COMMIT while blocked cannot proceed because it must first acquire the lock.

4. Final Answer:

   The waiting transaction issues a COMMIT -> Option C

5. Quick Check:

   Waiting means blocked; only blocking transaction actions help [OK]

Hint: Only blocking transaction actions unblock waiting transaction [OK]

Common Mistakes:

• Thinking waiting transaction can commit while blocked
• Assuming waiting state ends without lock release
• Confusing roles of blocking and waiting transactions