About the new parameter db_unrecoverable_scn_tracking

Db_unrecoverable_scn_tracking This parameter is from the 11.2.0.2 only, see the official document is described as follows:

Default value	true
modifiable	ALTER SESSION,ALTER SYSTEM
range of values	true | False
basic	no
Oracle RAC	Multiple instances must has the same value

DB_UNRECOVERABLE_SCN_TRACKINGEnables or disables the tracking of unrecoverable ( NOLOGGING ) Direct-path Insert and load operations.

When the value was set totrue, updates is made to the controlfile that maintains theV$DATAFILE.UNRECOVERABLE_CHANGE#andV$DATAFILE.UNRECOVERABLE_TIMEColumns. When the value was set tofalse, updates is not made to the controlfile. Setting This parameter tofalseMay improve performance of Direct-pathNOLOGGINGOperations.

----------------The default value of this parameter is true, if set to False, update operations with nologging cannot be updated to the control file.Performance of the NOLOGGINGload operation could is limited by the control file write I/O.If set to Flase, the performance of the direct path nologging will be increased.

Multiple instances must have the same value. Can be found from the following columns of V$datafile:

unrecoverable_change#
Unrecoverable_time
First_nonlogged_scn
First_nonlogged_time

This parameter has a bug on 11.2.0.2 and the official bug is as follows:

Bug 12360160-alter system/session of db_unrecoverable_scn_tracking has no effect (document ID 12360160.8)

Dynamically changing db_unrecoverable_scn_tracking with

Alter SESSION or ALTER SYSTEM have no effect on the value used. Rediscovery notes:the db_unrecoverable_scn_tracking Init.ora parameter can be modified dynamically and the change have no Effect The code uses the value from instance startup, and this startup value determines whether the unrecoverable Scn/timestamp I S recorded in the Controlfile (datafile sections) for Nologging writes.WorkaroundIf db_unrecoverable_scn_tracking is set to TRUE at startup, then event 10359 Level 1 can be used to dynamically disable (t Hen later dynamically enable) unrecoverable Scn/timestamp tracking in the controlfile:alter system set events ' 10359 Trace name Context forever, Level 1 '; Alter system set Events ' 10359 Trace name context off ';But, if Db_unrecoverable_scn_tracking was set to FALSE at startup, there was no workaround to dynamically over-ride this set Ting ie the unrecoverable scn/timestamp won't be tracked.

This bug has already been fixed on 11.2.0.3.

About the new parameter db_unrecoverable_scn_tracking