有朋友公司数据库由于_use_single_log_writer参数,导致 异常断电之后,数据库无法启动,报ORA-600 [kcrfrgv_nextlwn_scn]错误，通过分析是由于该参数导致.
DESCRIPTION
Oracle 12c introduces a new default feature of using multiple LGWRs which may lead to DEADLOCK / Database Hang or ORA-742 “Log read detects lost write” or ORA-600 [kcrfrgv_nextlwn_scn] during instance OPEN or ORA-600 [krr_process_read_error_2] during Recovery on IBM AIX and potentially on HPUX Itanium 64bit.
The database may become unusable and fail to be OPEN.
OCCURRENCE
This issue is specific to RDBMS version 12c (12.1.0.1 or 12.1.0.2) where the new default feature of using multiple LGWRs is introduced.
It affects databases on IBM AIX and potentially on HPUX Itanium 64bit
SYMPTOMS
ORACLE on IBM AIX or HPUX Itanium 64bit with RDBMS Version 12c.
DEADLOCK or ORA-742 “Log read detects lost write” or ORA-600 [kcrfrgv_nextlwn_scn] during instance OPEN or ORA-600 [krr_process_read_error_2] during Recovery caused by bug 21915719.
PMON may terminate the instance while extensive block recovery is being performed.
A DEADLOCK example is with LG0[n] waiting on ‘LGWR worker group ordering’. Example from a System State Dump trace file:
SO: 0x7000101f95ad720, type: 4, owner: 0x7000101f84195f8, flag: INIT/-/-/0x00
if: 0x3 c: 0x3
proc=0x7000101f84195f8, name=session, file=ksu.h LINE:13590 ID:, pg=0
conuid=0
(session) sid: 865 ser: 1 trans: 0x0, creator: 0x7000101f84195f
Current Wait Stack:
0: waiting for ‘LGWR worker group ordering’
lwn_id=0x58, phase=0x1, =0x0
wait_id=4947 seq_num=4948 snap_id=1
wait times: snap=13 min 21 sec, exc=13 min 21 sec, total=13 min 21 sec
wait times: max=infinite, heur=13 min 21 sec
wait counts: calls=1 os=267
in_wait=1 iflags=0x5a0
There is at least one session blocking this session.
Dumping 1 direct blocker(s):
inst: 1, sid: 817, ser: 1
Dumping final blocker:
inst: 1, sid: 817, ser: 1
There are 730 sessions blocked by this session.
.
.
PROCESS 17: LG00
SO: 0x7000101f85bcc60, type: 4, owner: 0x7000101f93eeb20, flag: INIT/-/-/0x00
if: 0x3 c: 0x3
proc=0x7000101f93eeb20, name=session, file=ksu.h LINE:13590 ID:, pg=0
conuid=0
(session) sid: 817 ser: 1 trans: 0x0, creator: 0x7000101f93eeb20
ksuxds FALSE at location: 0
service name: SYS$BACKGROUND
Current Wait Stack:
0: waiting for ‘LGWR worker group ordering’
lwn_id=0x56, phase=0x1, =0x0
wait_id=1630680 seq_num=57841 snap_id=1
wait times: snap=13 min 21 sec, exc=13 min 21 sec, total=13 min 21 sec
wait times: max=infinite, heur=13 min 21 sec
wait counts: calls=2 os=268
in_wait=1 iflags=0x15a0
There is at least one session blocking this session.
Dumping 1 direct blocker(s):
inst: 1, sid: 865, ser: 1
Dumping final blocker:
inst: 1, sid: 865, ser: 1
The instance may fail to OPEN with errors ORA-600 [kcrfrgv_nextlwn_scn] and/or ORA-600 [krr_process_read_error_2]:
ORA-00600: internal error code, arguments: [krr_process_read_error_2],
Alter database open fails with:
ORA-00600: internal error code, arguments: [kcrfrgv_nextlwn_scn] …..
ORA-600 signalled during: ALTER DATABASE OPEN…
WORKAROUND
Disable the new feature of multiple LGWR slave processes by proactively setting _use_single_log_writer=true.
Setting _use_single_log_writer = true is a safe workaround; it is the behavior before 12c where multiple LGWR slave groups were not available.
— Restart the database or all instances of the RAC database
Note that while _use_single_log_writer=true is not set, then error ORA-600 [kcrfrgv_nextlwn_scn] might be produced avoiding the database to OPEN. Once the problem is introduced, _use_single_log_writer=true may not fix it. _use_single_log_writer = true prevents inconsistencies in the redo log to be introduced which causes that error.
If the parameter does not help, because the problem was already introduced when _use_single_log_writer=true had not been proactively set, then Point in Time Recovery (PITR) or Flashback Database are the options to recover from this situation.
