What Is a B-tree Indexes in Oracle Database?
Oracle B-tree indexes keep keys ordered in branch and leaf blocks. Leaf entries identify rows by ROWID and support equality, range, and ordered retrieval.
How the B-tree Indexes Algorithm Works
Oracle B-tree indexes keep keys ordered in branch and leaf blocks. Leaf entries identify rows by ROWID and support equality, range, and ordered retrieval.
When to Use B-tree Indexes
Selective OLTP lookups, joins, range scans, unique keys, and ordered retrieval.
How to Create a Oracle Database B-tree Indexes
Review data quality, existing structures, feature support, build time, and deployment requirements before creating an index on a production table.
CREATE INDEX orders_created_at_ix ON orders (created_at);B-tree Indexes Query Example
This example demonstrates the matching query shape. Check the execution plan to confirm that the engine can use the index.
SELECT order_id FROM orders WHERE created_at >= DATE '2026-01-01' ORDER BY created_at;Queries Supported by B-tree Indexes
Selective OLTP lookups, joins, range scans, unique keys, and ordered retrieval. A similar-looking predicate may not use the same access path; operators, expressions, key order, and data type all matter.
Read Performance, Storage, and Write Costs
Entries consume space and require DML maintenance; random inserts can split blocks. Indexes reduce some search work but require storage and add maintenance to writes.
B-tree Indexes Limitations and Common Mistakes
Functions on columns, stale statistics, or low selectivity can make an index scan unattractive.
Do not assume that an index being present means the optimizer chose it or that the query became selective.
How to Measure and Tune B-tree Indexes
Use DBMS_XPLAN.DISPLAY_CURSOR with actual rows and buffer gets; keep statistics representative.
Compare representative plans and timings before and after, including concurrent writes and realistic data volumes.
B-tree Indexes Questions
Will the database always use this index?
No. The optimizer weighs selectivity, estimated costs, statistics, cache state, and the amount of data returned.
What should I verify before production?
Confirm version support, query compatibility, write overhead, build/rollback procedures, and index behavior during backup and recovery.
Official Oracle Database Index Documentation
Check Oracle Database Concepts: Indexes and Index-Organized Tables for release-specific requirements and supported operators.