Answer
REPEATABLE READ ensures consistent snapshots but not full phantom protection. SERIALIZABLE with SSI is required to prevent anomalies.
Quick Answer
REPEATABLE READ in PostgreSQL uses MVCC snapshot isolation. The transaction sees the database as it was at the START of the transaction - later committed changes are invisible. Prevents dirty reads and non-repeatable reads. Serialization anomalies are still possible (phantom reads don't occur because PostgreSQL uses snapshot-based, not lock-based, isolation). Use READ COMMITTED (default) for most cases; REPEATABLE READ for reporting transactions.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ