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Why Has the GATHER_STATS_JOB been removed in 11g and onward?

Oracle Database 10g introduced the concept automated maintenance task execution during maintenance windows implemented via a WEEKNIGHT_WINDOW and WEEKEND_WINDOW schedule. This included statistics collection by means of the GATHER_STATS_JOB.

In Oracle Database 11g and onward, the WEEKNIGHT_WINDOW and WEEKEND_WINDOW schedules (defined in Oracle Database 10g) are replaced with daily maintenance windows (such as  SUNDAY_WINDOW, MONDAY_WINDOW etc). These were replaced in order to add increased flexibility and manageability. One can query dba_scheduler_windows to check the window definitions.

Automatic Maintenance Tasks (including the automated Optimizer Statistics Gathering task) are defined to execute within these daily windows. Using Enterprise Manager is the preferred way to control Automatic Maintenance Tasks, although the DBMS_AUTO_TASK_ADMIN package can also be used.

'Automatic Maintenance Tasks Management ' is an 11g new feature and was implemented to increase the  flexibility of statistics collection and to avoid potential resourcing issue when maintenance jobs run  alongside user operations.  Maintenance operations can potentially use a lot of resource which may, in extreme cases, affect other jobs. To address this, in 11g, maintenance operations are closely linked to resource manager to manage the resources that are used and share them more efficiently.

For more information on how to setup and maintain automatic statistics collection see:
Document 1233203.1 FAQ: Automatic Statistics Collection
There is an overview description of the feature in the:
Oracle Database New Features Guide
11g Release 1 (11.1)
Part Number B28279-03
"This feature ensures that work during maintenance operations is not affected and that user activity gets the necessary resources to complete."  By spreading the workload over multiple weeknights and managing the resource usage, this feature provides the flexibility to allow maintenance jobs to complete in a timely fashion and for user operations to be unaffected.

Users are still completely free to define other maintenance windows and change start times and durations for the daily maintenance windows.

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