Some implied parameters changing after oracle 11.2.0.2

1 query implicit parameters

SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ

FROM SYS.x$ksppi x, SYS.x$ksppcv y

WHERE x.inst_id = USERENV ('Instance')

AND y.inst_id = USERENV ('Instance')

AND x.indx = y.indx

AND x.ksppinm LIKE'% & par%'

2 _ datafile_write_errors_crash_instance

11.2.0.2 added. Default is true. If a write error occurs, the instance is disabled directly. It used to be offline.

3 _ use_adaptive_log_file_sync

This parameter defaults to false in versions 11.2.0.1 and 11.2.0.2.

Starting from 11.2.0.3, the default value of this parameter is true, which means that the "adaptive log synchronization mechanism" is enabled.

When the parameter change is enabled, the log synchronization mechanism will switch between the two modes.

This parameter determines how the foreground/user session and LGWR processes know that the commit operation is complete (that is, the redo write log file is complete).

Post/wait, traditional method for posting completion of writes to redo log

Traditionally, before 11.2.0.3, user session waited for LGWR to tell redo to write to log file, passively.

Advantages: post/wait mode, user session can almost immediately find that redo has been brushed to disk.

Polling, a new method where the foreground process checks if the LGWR has completed the write.

A new way to actively monitor whether the LGWR has completed writing, active mode. This approach is slower than Post/wait, but it can save CPU resources.

Pros: when the commit is complete, LGWR notifies many user session of the commit completion message, which consumes a lot of CPU.

The Polling method uses Zhu Yong to monitor the release of LGWR and write to redo, so the CPU resources occupied by LGWR are released.

4 _ external_scn_rejection_threshold_hours

The default value for this parameter is 24 for 11.2.0.2 and above, and 744 for other versions. This increases the threshold of Headroom for databases below 11.2.0.2.

5 _ minimum_giga_scn

11.2.0.2 it is invalid after the relevant patch is applied; in addition, alter session set events' 10015 trace name adjust_scn level XXX' can't push SCN. Check SCN.

Recommended method to promote SCN 1:

1. When the data block is 8k, the size of the control file is 16k

2. Find the Controlfile Checkpointed at scn, the offset is 60 of the first block, such as 0 × 4060, and then the specific location is the 9th to 14th byte of 0 × 4060.

3. Find the first line of the first block, such as 0 × 4000, change the flag with offset 15 from 0 × 04 to 0 × 00, and clear all the checksum values (offset = 16, 17) at the same time.

Recommended method for promoting SCN 2:

"oradebug poke" allows you to modify a given region of memory (length of memory is limited to size of scalar C types)

SQL > col current_scn for 999999999999999999 help SQL > select current_scn from vault database; CURRENT_SCN- 12414232664SQL > select to_char (CHECKPOINT_CHANGE#,'XXXXXXXXXXXX') from vault database; TO_CHAR (CHECK- 2E3F154CESQL > oradebug dumpvar sga kcsgscn_kcslf kcsgscn_ [5000C974, 5000C994) = 00000002 E3F243A0 05AC1DA5 000000000000000000000000000000000000000000000000000000000000000000000xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx