## How often we should gather stats in Oracle?

Since Oracle 11g statistics are gathered automatically by default. Two Scheduler windows are predefined upon installation of Oracle Database: WEEKNIGHT_WINDOW starts at 10 p.m. and ends at 6 a.m. every Monday through Friday. WEEKEND_WINDOW covers whole days Saturday and Sunday.

**What is the use of gather schema statistics in Oracle?**

You should gather statistics periodically for objects where the statistics become stale over time because of changing data volumes or changes in column values. New statistics should be gathered after a schema object’s data or structure are modified in ways that make the previous statistics inaccurate.

**How often should I generate statistics in Oracle?**

If the size and data distribution of your tables change frequently, then you should generate these statistics regularly to ensure the statistics accurately represent the data in the tables. Oracle generates statistics using the following techniques: Estimation based on random data sampling Exact computation

### What Statistics does Oracle gather for partitioned indexes?

For a partitioned index, Oracle does not gather any table or column statistics while creating the index or rebuilding its partitions. While creating a partitioned index, Oracle gathers index statistics for each partition and for the entire index. If the index uses composite partitioning, then Oracle also gathers statistics for each subpartition.

**How does Oracle gather Index statistics when rebuilding an index?**

While rebuilding a partition or subpartition of an index, Oracle gathers index statistics only for that partition or subpartition. To ensure correctness of the statistics, Oracle always uses base tables when creating an index with the COMPUTESTATISTICSoption, even if another index is available that could be used to create the index.

**How does Oracle identify tables with stale statistics?**

This includes the approximate number of inserts, updates, and deletes for that table since the last time statistics were gathered. Oracle uses this data to identify tables with stale statistics. View the data Oracle obtains from monitoring these tables by querying the USER_TAB_MODIFICATIONSview. Note: