[Solved] In PostgreSQL's MVCC, what does a transaction see when it queries data? — Ans: Only the committed data as of the transaction start time | PostgreSQL

PostgreSQL - Transactions and Concurrency

In PostgreSQL's MVCC, what does a transaction see when it queries data?

AAll data including uncommitted changes from other transactions

BOnly the data modified by itself

COnly the committed data as of the transaction start time

DThe latest data regardless of commit status

Step-by-Step Solution

Solution:

Step 1: Recall MVCC snapshot behavior
Each transaction sees a consistent snapshot of the database as it was at the start of the transaction.
Step 2: Understand visibility rules
This means it sees only committed data up to that point, ignoring uncommitted changes from others.
Final Answer:
Only the committed data as of the transaction start time -> Option C
Quick Check:
Transaction snapshot = committed data at start [OK]

Quick Trick: Transactions see a fixed snapshot at start [OK]

Common Mistakes:

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In PostgreSQL's MVCC, what does a transaction see when it queries data?