PostgreSQL Query Plans for Reading Tables

This article delves into the concept of Scan Nodes in PostgreSQL executor's query plan tree, which are used to read data from tables. There are four types of Scan nodes: Sequential Scan, Parallel Sequential Scan, Index Scan, and Index Only Scan. The planner decides the type of scan based on factors such as the data sought by the query, availability of indexes, and expected performance improvement. Each type of scan has its own advantages and disadvantages, with sequential scans being efficient for small tables while index scans are effective in retrieving a small number of relevant rows from large tables. The article also provides examples to illustrate the use of each type of Scan node.