Clustering against an index

In this recipe, we will be discussing a table reordering strategy based on an index, which will improve the query performance for a certain time.

Getting ready

In PostgreSQL, we have a utility command called CLUSTER that is like VACUUM. It will do some kind of table reorganization by acquiring access exclusive locks on the table. The CLUSTER command will create a new physical table by aligning its pages in the order of the mentioned index. An advantage of doing this is to avoid the index lookup overhead during the index scan, since the table itself is in ordered. Another benefit of doing this is removing all dead tuples from the table and index.

Note

Running the CLUSTER command during the business hours is not recommended as it will acquire the access exclusive lock, which will block the incoming queries on the table. Also, the CLUSTER operation requires an additional amount of disk space for the newly created table and indexes, which will drop the old table and...