What index is used by default in PostgreSQL and why B-tree and not a red-black tree?

In PostgreSQL, the default index type used is B-tree.

Reasons for choosing B-tree:

• B-tree is a balanced tree with ordered keys, which provides efficient search, insertion, and deletion in logarithmic time.
• Supports range queries (e.g., BETWEEN, >, <), which are important for most use cases.
• Scales well with increasing data volume.

Why not red-black tree?

• Red-black tree is a binary balanced tree, suitable for main memory, but not optimal for disk structures.
• B-tree is optimized for working with large blocks of data on disk, minimizing read/write operations.
• Minimizing disk accesses is crucial in databases, making B-tree more suitable for indexes.

Thus, B-tree is a compromise between search efficiency and optimization for disk subsystems, making it an ideal choice for indexes in PostgreSQL.