PostgreSQL Row Locking: Row Exclusive Lock Explained

When performing UPDATE, INSERT, or DELETE operations in PostgreSQL, the database automatically acquires a specific lock to ensure data consistency. The correct lock type for preparing row-level updates is ​Row Exclusive Lock (ROW EXCLUSIVE)​.

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Key Insights from the Answer

1. ​Row Exclusive Lock (D. Row Exclusive Lock)​​

• ​Purpose: Acquired automatically during INSERT, UPDATE, or DELETE commands.
• ​Behavior:
  • Blocks conflicting DDL operations (e.g., ALTER TABLE).
  • Allows concurrent SELECT queries (no read blocking).
  • Prevents other transactions from acquiring incompatible locks (e.g., SHARE UPDATE EXCLUSIVE).

2. ​Comparison with Other Lock Types

Technical Details

• ​Scope:
  • ​Table-level lock: Acquired on the target table before row-level locks.
  • ​Row-level locks: Applied to individual rows being modified (e.g., FOR UPDATE).
• ​Avoid Conflicts:
  • Do not run DDL operations (e.g., adding indexes) concurrently with updates.
  • Use pg_locks to diagnose locking issues:

SELECT * FROM pg_locks WHERE relation = 'your_table'::regclass;

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Why This Matters

Choosing the right lock type ensures:

1. ​Data Integrity: Prevents race conditions during concurrent updates.
2. ​Performance: Minimizes contention between OLTP workloads and maintenance tasks.

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