PostgreSQL - Transactions and Concurrency
In PostgreSQL, when two transactions simultaneously attempt to update the same row, how does MVCC handle this conflict?
In PostgreSQL, when two transactions simultaneously attempt to update the same row, how does MVCC handle this conflict?
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Step-by-Step Solution
Solution:
Step 1: Understand MVCC concurrency
MVCC allows concurrent reads but serializes conflicting writes.Step 2: Conflict resolution
When two updates conflict, one transaction waits or aborts with serialization error.Final Answer:
One transaction waits or fails due to a serialization conflict -> Option CQuick Check:
Conflicting writes cause wait or error [OK]
Quick Trick: Conflicting updates cause wait or error [OK]
Common Mistakes:
- Assuming simultaneous updates merge automatically
- Believing both updates succeed without conflict
- Thinking first transaction always rolls back
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