In PostgreSQL, what happens if a transaction running under REPEATABLE READ tries to update a row that was modified by another concurrent transaction?

easy📝 Conceptual Q2 of 15

PostgreSQL - Transactions and Concurrency

In PostgreSQL, what happens if a transaction running under REPEATABLE READ tries to update a row that was modified by another concurrent transaction?

AThe transaction immediately overwrites the other transaction's changes.

BThe transaction waits until the other transaction commits or rolls back.

CThe transaction raises a serialization failure error.

DThe transaction ignores the conflict and proceeds.

Step-by-Step Solution

Solution:

Step 1: Understand locking in REPEATABLE READ
PostgreSQL uses row-level locks; conflicting updates cause waiting.
Step 2: Behavior on concurrent updates
The transaction waits for the other to finish to avoid conflicts.
Final Answer:
The transaction waits until the other transaction commits or rolls back. -> Option B
Quick Check:
Concurrent update = Wait for lock release [OK]

Quick Trick: Conflicting updates wait, no immediate overwrite [OK]

Common Mistakes:

Assuming immediate overwrite
Expecting error instead of wait
Ignoring locking behavior

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In PostgreSQL, what happens if a transaction running under REPEATABLE READ tries to update a row that was modified by another concurrent transaction?

Step 1: Understand locking in REPEATABLE READ

Step 2: Behavior on concurrent updates

Final Answer:

Quick Check:

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