How to check if an index is effective in Oracle?

To check if indexes are effective in Oracle database, you can use the following methods: 1. Use EXPLAIN PLAN: Prefix your query with EXPLAIN PLAN FOR, execute the query, and then use SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY); to view the execution plan. The plan will show whether indexes are being used, and in what way (full table scan, index scan, etc.). 2. Use SQL Trace: Utilize Oracle’s SQL Trace feature to track the execution of queries, including index usage. Enabling SQL Trace allows you to access detailed execution information, including index usage, by examining the trace file. 3. Use SQL Developer or other performance monitoring tools: Oracle offers various performance monitoring tools like SQL Developer to view index usage. These tools typically provide a visual interface for easily checking the execution plan and index usage of queries. 4. Use DBA views: Query Oracle database’s DBA views to access index usage information. You can query DBA_INDEXES view, DBA_SEGMENTS view, etc., to view statistical information for indexes such as scan count and access count. In conclusion, these are some common methods to check index usage in Oracle database. Depending on specific needs and circumstances, choose the appropriate method to determine if indexes are effective.