What types of indexes exist in PostgreSQL? How does B-tree differ from a binary tree?

In PostgreSQL, there are several types of indexes, the main ones are:

• B-tree — the most common type of index, used for fast equality and range searches.
• Hash — an index for quick equality searches, but less versatile than B-tree.
• GIN (Generalized Inverted Index) — an index for full-text search and working with arrays.
• GiST (Generalized Search Tree) — a versatile index supporting various data types, such as geometric.
• SP-GiST — a specialized GiST for specific data structures.
• BRIN (Block Range INdexes) — a compact index for large tables with ordered data.

Difference between B-tree and binary tree:

B-tree is a balanced tree with multiple keys in each node and multiple children, allowing data to be stored in sorted order and efficiently utilizing disk space. Unlike a classic binary tree, where each node has no more than two children, B-tree has many children (usually from several dozen to hundreds), reducing the tree's height and the number of disk read operations.

Thus, B-tree is optimized for working with large volumes of data on disk, minimizing disk access, while a binary tree is suitable for in-memory operations and is inefficient for large datasets.