[Solved] Why does this transaction fail under Serializable isolation?BEGIN;SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;SELECT balance FROM accounts WHERE id = 1;UPDATE accounts SET balance = balance + 50... | PostgreSQL

PostgreSQL - Transactions and Concurrency

Why does this transaction fail under Serializable isolation?
BEGIN; SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; SELECT balance FROM accounts WHERE id = 1; UPDATE accounts SET balance = balance + 50 WHERE id = 1; COMMIT;
Meanwhile, another transaction updated the same row and committed.

ADeadlock detected between transactions

BSyntax error in SET TRANSACTION command

CSerialization failure due to concurrent conflicting update

DThe SELECT statement causes a lock timeout

Step-by-Step Solution

Solution:

Step 1: Understand Serializable Conflict Detection
The first transaction reads and updates a row that another transaction modified concurrently, causing a conflict.
Step 2: Identify Failure Reason
PostgreSQL aborts one transaction with a serialization failure to maintain consistency.
Final Answer:
Serialization failure due to concurrent conflicting update -> Option C
Quick Check:
Concurrent update conflict = Serialization failure [OK]

Quick Trick: Concurrent conflicting updates cause serialization failures [OK]

Common Mistakes:

Confusing serialization failure with syntax error
Assuming deadlock instead of serialization failure
Thinking SELECT causes lock timeout

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Why does this transaction fail under Serializable isolation?

Step 1: Understand Serializable Conflict Detection

Step 2: Identify Failure Reason

Final Answer:

Quick Check:

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