Oracle 12c SCN推进方法汇总（二）之EVENT

SQL> select current_scn from v$database;

CURRENT_SCN
-----------
    5100732
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

修改pfile,添加参数

[oracle@devin-enmo script]$ vi /u01/app/oracle/product/12.2/dbhome_1/dbs/inithkora.ora 
_allow_resetlogs_corruption=true
*.event="21307096 trace name context forever, level 5"

PFILE启动

[oracle@devin-enmo script]$ sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Mon Feb 1 14:17:21 2021

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup mount  pfile='/u01/app/oracle/product/12.2/dbhome_1/dbs/inithkora.ora'
ORACLE instance started.

Total System Global Area  268435456 bytes
Fixed Size                  8619496 bytes
Variable Size             201329176 bytes
Database Buffers           50331648 bytes
Redo Buffers                8155136 bytes
Database mounted.
SQL> recover database using backup controlfile until cancel;
ORA-00279: change 5106151 generated at 02/01/2021 14:16:20 needed for thread 1
ORA-00289: suggestion : /u01/app/oracle/fast_recovery_area/1_1_1063364001.dbf
ORA-00280: change 5106151 for thread 1 is in sequence #1


Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
Media recovery cancelled.
SQL> alter database open resetlogs;

Database altered.

验证

SQL> select current_scn from v$database;

CURRENT_SCN
-----------
   10106627

事件21307096以百万为单位递增，如上LEVEL 5，SCN推进了500W。
根据LEVEL值不一样，数据库OPEN耗时也不一样，计算公式：

  level 1 Elapsed: 00:01:02.35
  level 2 Elapsed: 00:02:16.23
  level 6 Elapsed: 00:06:08.05
 
In general:  based on a 16k per second scn rate (16K/sec) , the open resetlogs time
would be at least (event level * 1000000 / 16000) seconds. Then level 1 would be at least 
62+ seconds and level 4095 would be 71+ hours !.