Insight 01.1
A foreign key ensures referential integrity, but it does not automatically create an index on the child table. Without an index, every update or deletion in the parent table requires a full table scan of the child table. In Oracle, a missing FK index often leads to massive locking issues and TM-Enqueue contention wait events.
In PostgreSQL, missing FK indexes are a primary cause of performance degradation during joins between related tables. A missing index on the foreign key prevents both systems from performing efficient 'ON DELETE CASCADE' operations. Furthermore, deadlocks can occur when Oracle attempts to lock the entire child table to verify integrity. In PostgreSQL, the index primarily boosts the speed of lookups whenever records in the parent table are updated. Rule of thumb: Every foreign key should be indexed unless the child table is extremely small (only a few rows). Composite keys (multi-column keys) require careful planning regarding the column order within the index. Modern monitoring scripts can automatically identify missing FK indexes before they cause production issues.
In summary: Indexing foreign keys is a best practice that prevents locks and drastically improves join performance.
Foreign Key Indizes
Foreign Key Indexes: Why they are indispensable in Oracle and PostgreSQL.
A foreign key ensures referential integrity, but it does not automatically create an index on the child table. Without an index, every update or deletion in the parent table requires a full table scan of the child table. In Oracle, a missing FK index often leads to massive locking issues and TM-Enqueue contention wait events.
In PostgreSQL, missing FK indexes are a primary cause of performance degradation during joins between related tables. A missing index on the foreign key prevents both systems from performing efficient 'ON DELETE CASCADE' operations. Furthermore, deadlocks can occur when Oracle attempts to lock the entire child table to verify integrity. In PostgreSQL, the index primarily boosts the speed of lookups whenever records in the parent table are updated. Rule of thumb: Every foreign key should be indexed unless the child table is extremely small (only a few rows). Composite keys (multi-column keys) require careful planning regarding the column order within the index. Modern monitoring scripts can automatically identify missing FK indexes before they cause production issues.
In summary: Indexing foreign keys is a best practice that prevents locks and drastically improves join performance.