Bug 16196536 - Many active undo extents with flashback Archive

刘泽宇

描述：
This bug is only relevant when using Flashback Data Archive (Oracle Total Recall)
A rapidly growing number of active undo extents may be seen in a non-RAC
(or former RAC) environment if Flashback Archive is being used.

This fix applies to RAC also; although the main part of the fix concerns single
instance recovery&recycling after being run as RAC, there are parts that
apply to both, RAC and non-RAC.

注意事项：
If the amount of active undo segments is growing very rapidly
AND
  "select * from SYS_FBA_BARRIERSCN" shows more than one instance (INST_ID)
  in a non-RAC environment, then you have likely hit this issue.

可用方法：
(as an example!)
a. backup the current record in sys_fba_barrierscn table
    SQL> create table csdba.sys_fba_barrierscn as select * from sys_fba_barrierscn;
b. Deleting information in the sys.sys_fba_barrierscn table where inst_id = 1
    SQL>   alter system set "_fbda_debug_mode"=8;
    SQL>   delete from sys.sys_fba_barrierscn where inst_id = 1;
    SQL>   commit;
    SQL>   alter system set "_fbda_debug_mode"=0;

c. flush the shared pool to make sure the memory is clean
    SQL>   alter system flush shared_pool;