Indexes can dramatically improve PostgreSQL read performance, but they are not free.
What an index does
An index is a data structure that helps PostgreSQL locate rows faster without scanning an entire table.
For most equality and range lookups, B-tree is the default index type.
When to add an index
Consider indexing columns used in:
WHEREfiltersJOINconditionsORDER BYclauses
Start from real slow-query data, not assumptions.
Avoid over-indexing
Each index adds storage overhead and slows down inserts/updates/deletes. Too many indexes can hurt overall throughput.
Verify with EXPLAIN
Use EXPLAIN (ANALYZE, BUFFERS) to compare query plans before and after indexing.
Key signs of improvement:
- Lower execution time
- Fewer shared buffer reads
- Better row estimate accuracy
Indexing is most effective when paired with query tuning and realistic workload testing.