Senior LevelPostgreSQL
How does Serializable Snapshot Isolation (SSI) prevent Write Skew anomalies without pessimistic locks?
❓ Interview Prompt: Explain Isolation Levels, Serializable Snapshot Isolation (SSI), SIREAD locks, Dependency Graph tracking, and preventing Write Skew anomalies.
Serializable Snapshot Isolation (SSI) provides true strict Serializability without pessimistic row locking ('SELECT FOR UPDATE'):
How SSI Works:
1
Tracks 'SIREAD' locks in shared memory to monitor data dependencies between concurrent transactions.
2
Detects read-write dependency cycles (rw-antidependencies).
3
If a Write Skew cycle occurs, aborts one transaction with '40001 serialization_failure', guaranteeing strict isolation!
Code Implementation Example
sql
-- Set transaction isolation level to SERIALIZABLE
BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
-- Queries execute under SSI optimistic concurrency control
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
COMMIT;💡Executing transactions under Serializable Snapshot Isolation (SSI).
🎯 Interview Key Takeaway
Use SERIALIZABLE isolation mode to prevent Write Skew anomalies, handling 40001 serialization_failure retries in code.
#SSI#Serializable#Write Skew#Isolation Levels#Senior
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