Does PostgreSQL Automatically Index Foreign Keys and Primary Keys?

Postgres Foreign Key and Primary Key Indexing

In PostgreSQL, the automatic creation of indexes on foreign keys and primary keys has varying behaviors.

Foreign Keys

PostgreSQL does not automatically create indexes on foreign key references. The referencing columns remain unindexed. You can manually create indexes on referencing columns if desired. This may enhance performance in certain scenarios, but it can also incur a slight overhead on DML operations.

Primary Keys

In contrast, PostgreSQL automatically creates indexes on both primary keys and unique constraints. These indexes enforce uniqueness and optimize access to rows based on the primary key values. The creation of these indexes is indicated by a NOTICE-level message in the system logs or psql output.

Identifying Indexes

To inspect the indexes on a table, you can use the d command. This command displays information about the table, including the list of indexes present.

Recommendations

Consider creating indexes on referencing foreign key columns if performance is a concern and the index is likely to be frequently used. However, creating unnecessary indexes can potentially slow down data modification operations. Therefore, it is important to carefully weigh the benefits of indexing against the potential performance impact.

The above is the detailed content of Does PostgreSQL Automatically Index Foreign Keys and Primary Keys?. For more information, please follow other related articles on the PHP Chinese website!