How can performance tuning and query optimization be done in PostgreSQL?

In PostgreSQL, performance tuning and query optimization can be achieved through the following methods:

1. Utilize appropriate indexes: Creating indexes can speed up query operations, especially for frequently queried fields. When determining which fields to index, consider using fields frequently used in the WHERE clause as well as the connection fields in JOIN operations.
2. Optimize queries: avoid full table scans and unnecessary JOIN operations, try to simplify the query statement, reduce unnecessary calculations and data transfer.
3. Choose appropriate data types: selecting suitable data types can reduce memory usage and improve query efficiency. Use integer data types as much as possible to store integer data, and avoid using character data types to store date and time data.
4. Adjusting the configuration parameters of PostgreSQL can improve performance, such as optimizing buffer sizes, concurrent connection numbers, and query optimization.
5. Analyze the query plan using EXPLAIN: By using the EXPLAIN command, you can review the execution plan of the query in order to optimize the query statement and prevent slow queries.
6. Regularly cleaning and optimizing the database can improve performance by removing unnecessary data and indexes, and performing VACUUM and ANALYZE operations.
7. Utilize appropriate tools and techniques such as the pg_stat_statements plugin to monitor query performance, use pg_stat_activity to view current active connections, for performance tuning and query optimization.