How to resolve the issue of a failed composite index in Oracle?

When an Oracle composite index fails, you can try the following solutions: 1. Rebuild the index: Use the ALTER INDEX statement to rebuild the index, which can solve index fragmentation issues and improve index efficiency. 2. Optimize the query statement: Check if the query statement can be optimized, such as using a more appropriate index column order, adding missing indexes, etc. 3. Recollect statistics: Use the statistics collection process in the DBMS_STATS package to update the statistics of tables and indexes to ensure that the Oracle optimizer can correctly choose indexes. 4. Adjust the query plan: If the index failure is caused by an incorrect query plan, you can use HINTS to specify the correct index to use. 5. Split the index: If some columns in the composite index have low usage frequency in queries, consider splitting these columns out and creating independent indexes to improve query efficiency. 6. Use covering indexes: For certain queries, using covering indexes can avoid table access operations, thereby improving query efficiency. 7. Adjust database parameters: If index failures occur frequently, consider adjusting some database parameters, such as increasing SGA size, adjusting optimizer parameters, etc. These are some common solutions. The specific solution may vary depending on the specific index failure situation, and analysis and adjustments based on the specific index failure situation are needed.