In Oracle 12c, indexes play a crucial role in optimizing query performance. When dealing with partitioned tables, partitioned indexes help improve access speed and efficiency. However, over time, these indexes may become fragmented or need rebuilding due to maintenance tasks such as partition operations (drop, merge, split, etc.). This article covers the methods to rebuild partition indexes in Oracle 12c.
When to Rebuild a Partition Index
Rebuilding a partition index is necessary in the following scenarios:
After dropping or truncating a partition.
After splitting or merging partitions.
When index fragmentation impacts performance.
When an index is marked as unusable after a DDL operation.
Methods to Rebuild a Partition Index
1. Rebuilding a Specific Partition of an Index
If only a specific partition of an index needs rebuilding, use the following SQL command:
ALTER INDEX index_name REBUILD PARTITION partition_name;
Example:
ALTER INDEX sales_idx REBUILD PARTITION sales_q1_2024;
This command rebuilds the sales_q1_2024 partition of the sales_idx index.
2. Rebuilding the Entire Index
If all partitions of an index need rebuilding, you can use:
ALTER INDEX index_name REBUILD;
Example:
ALTER INDEX sales_idx REBUILD;
This rebuilds the entire sales_idx index.
3. Rebuilding All Partitions of an Index
To rebuild all partitions explicitly, run:
ALTER INDEX index_name REBUILD PARTITION ALL;
Example:
ALTER INDEX sales_idx REBUILD PARTITION ALL;
This ensures that all partitions of sales_idx are rebuilt.
4. Rebuilding a Subpartitioned Index
For indexes on subpartitioned tables, rebuild a specific subpartition using:
ALTER INDEX index_name REBUILD SUBPARTITION subpartition_name;
Example:
ALTER INDEX sales_idx REBUILD SUBPARTITION sales_jan_2024;
This rebuilds the sales_jan_2024 subpartition of the sales_idx index.
Considerations When Rebuilding Indexes
Online vs. Offline Rebuild:
By default, index rebuilding is an offline operation, meaning the index is unavailable during the rebuild.
Use the ONLINE keyword to keep the index available:
ALTER INDEX sales_idx REBUILD PARTITION sales_q1_2024 ONLINE;
Parallelism:
To speed up index rebuilding, use parallel execution:
ALTER INDEX sales_idx REBUILD PARTITION sales_q1_2024 PARALLEL 4;
Tablespace Considerations:
If necessary, specify a different tablespace during the rebuild:
ALTER INDEX sales_idx REBUILD PARTITION sales_q1_2024 TABLESPACE new_tablespace;
Verifying Index Status
After rebuilding, check the index status using:
SELECT INDEX_NAME, PARTITION_NAME, STATUS FROM USER_IND_PARTITIONS WHERE INDEX_NAME = 'SALES_IDX';
A status of USABLE confirms that the rebuild was successful.
Conclusion
Rebuilding partitioned indexes in Oracle 12c is essential for maintaining database performance and integrity. By understanding when and how to rebuild indexes—whether for individual partitions, all partitions, or subpartitions—you can ensure optimal query execution and efficient data management. Always verify index status after rebuilding and consider online rebuild options for minimal disruption in a production environment.