7. HOT and Index-Only Scans

This chapter describes two advanced features that assist table maintenance and optimize index scans: Heap Only Tuple (HOT) and Index-Only Scans.

Although these two features target different aspects of query optimization, both closely interact with the VACUUM processing mechanism. HOT was introduced to mitigate table bloating caused by frequent UPDATE operations and to minimize the need for immediate page-level VACUUMing. Index-Only Scans utilize the Visibility Map — maintained by the VACUUM process — to skip visibility checks on table pages and retrieve data directly from the index.

Building on the concepts of query execution, concurrency control, and VACUUM processing introduced in earlier chapters, this chapter explores these mechanisms.