In PostgreSQL, selecting the appropriate transaction isolation level is crucial for balancing data consistency with concurrency. Here are recommended patterns for isolation levels that help reduce blocking:

• Use Read Committed for Most Applications:
  • The default level, Read Committed, offers a good balance between consistency and concurrency, allowing transactions to see only committed changes made by others. It minimizes locking by not holding locks on read operations, reducing the chance of blocking other transactions.
• Opt for Repeatable Read for Higher Consistency Without Significant Locking:
  • Repeatable Read provides a consistent view of the database to each transaction and prevents non-repeatable reads. PostgreSQL implements it in a way that avoids most of the locking issues common in other databases, using versioning instead of locks for most operations.
• Reserve Serializable for Critical Sections:
  • The Serializable level guarantees strict transaction serialization, suitable for transactions that require absolute consistency. Use it sparingly for critical sections of your application where data integrity is paramount, as it can lead to increased blocking and potential transaction rollbacks due to conflicts.
• Consider Statement-Level Consistency for Reporting:
  • For long-running reporting queries that can tolerate some level of inconsistency, consider running them at a lower isolation level or using explicit locking hints to avoid blocking updates and other critical transactions.
• Apply Locking Hints Where Appropriate:
  • In cases where finer control over locking behavior is needed, PostgreSQL's explicit locking mechanisms (FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE, FOR KEY SHARE) can be used within transactions to lock specific rows or tables, potentially reducing the need for higher isolation levels and thus minimizing blocking.

By carefully choosing the isolation level and considering the use of explicit locking when necessary, it's possible to significantly reduce blocking, thereby improving the performance and concurrency of PostgreSQL-based applications.