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Bug 8895202 - ORA-1555 / ORA-600 [ktbdchk1: bad dscn] in Physical Standby after switch-over [ID 8895202.8]  

2011-12-19 11:33:29|  分类: ORACLE BUG |  标签: |举报 |字号 订阅

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Bug 8895202  ORA-1555 / ORA-600 [ktbdchk1: bad dscn] in Physical Standby after switch-over
 This note gives a brief overview of bug 8895202.
 The content was last updated on: 12-DEC-2011
 Click here for details of each of the sections below.
Affects:
Product (Component) Oracle Server (Rdbms)
Range of versions believed to be affected Versions BELOW 12.1
Versions confirmed as being affected
11.2.0.1
11.1.0.7
Platforms affected Generic (all / most platforms affected)

Fixed:
This issue is fixed in
12.1 (Future Release)
11.2.0.2 (Server Patch Set)


Symptoms:

Related To:

Corruption
Corruption (Logical)
Error May Occur
Internal Error May Occur (ORA-600)
ORA-1555
ORA-600 [ktbdchk1: bad dscn]

Physical Standby Database / Dataguard
_ktb_debug_flags

Description
ORA-1555 / ORA-600 [ktbdchk1: bad dscn] / ktbGetDependentScn errors /  
Dependent scn violations as itl has higher commit scn than block scn.
This happens in a Physical Standby database right after a switch-over
to the Primary database role.
DBVERIFY with the fix of Bug 7517208 reports this logical SCN inconsistency  
with error:
itl[<itl_id>] has higher commit scn(aaaa.bbbb) than block scn (xxxx.yyyy)
Page <Block#> failed with check code 6056
There is NOT DATA CORRUPTION in the block.     
Workaround     
This fix is the workaround.
This fix does not prevent to have a higher ITL SCN than the commit scn (csc).    
The fix workarounds the problem by using parameter _ktb_debug_flags = 8
as described in step 4 below and SCN problem is fixed when the block is
cleaned out (a block update may force it).
While blocks are not touched,
dbverify may still report the logical scn problem with code 6056 as in the
dbverify example above.
Steps to enable this fix:     
***** Additional actions after installing the patch ******         
To enable this patch - has to be done clusterwide by bringing all instances   
down as the scn-wrap will be advanced once.
1. Apply the patch.         
For 11.2.0.2 the fix is already included there but it needs to be enabled;
so the next steps also apply to 11.2.0.2.
2. Bump scn wrap in the database to avoid the error for all the affected      
blocks:
a. set the following parameter in the init.ora file
_allow_error_simulation = TRUE
_smu_debug_mode=268435456 (increases scn wrap by 1)
b. start the database.
If the database cannot be shutdown due to availability go directly
to step 4 (this will fix block by block when there is a block cleanout).
Note that bumping the SCN avoids the errors but dbverify may
still report the scn inconsistency which is fixed when the
block is cleaned out while _ktb_debug_flags=8 is active in the instance.
3. Remove both parameters added in the step 2.       
MAKE SURE TO REMOVE THE PARAMETERS OTHERWISE SCNWRAP ADVANCE WILL INCREASE
ACROSS EVERY STARTUP.
4. Set parameter _ktb_debug_flags = 8     
THIS IS CRUCIAL AS THIS ENABLES THE FIX.
_ktb_debug_flags=8 NEEDS TO REMAIN in the database to ENABLE THE FIX.
If the database is already open and cannot be shutdown, the parameter
can be dynamically set with:
alter system set "_ktb_debug_flags"=8;
Blocks are repaired when they are cleaned out. Trace file may show a
message like:
Healing Corrupt DLC ITL objd:%d objn:%d tsn:%d rdba:<rdba> itl:%d
option:%d xid:<xid> cmtscn:<scn> curscn:<scn>
There is no danger in keeping _ktb_debug_flags=8 all the time. It just
gets triggered on by invalid scn in itl.
5. Restart the database.     
Notes:
The above steps are to be done on the current primary database. For the
standby, all steps except #2 and #3 need to be performed. The change to the
SCN wrap will be propagated to the standby via the recovery of the primary's redo. The "_ktb_debug_flags"=8 ensures the fix will still be in place for role changes in the future. Although this fix is included in 11.2.0.2, it has to be enabled by setting "_ktb_debug_flags"=8.

HOOKS ERROR:ORA-1555 "OERI:ktbdchk1: bad dscn" "PARAMETER:_ktb_debug_flags" LIKELYAFFECTS XAFFECTS_11.1.0.6 XAFFECTS_V11010006 AFFECTS=11.1.0.6 XAFFECTS_11.1.0.7 XAFFECTS_V11010007 AFFECTS=11.1.0.7 XAFFECTS_11.2.0.1 XAFFECTS_V11020001 AFFECTS=11.2.0.1 XPRODID_5 PRODUCT_ID=5 PRODID-5 RDBMS XCOMP_RDBMS COMPONENT=RDBMS TAG_CORR TAG_CORR/LOG TAG_ERROR TAG_OERI TAG_STANDBY CORR CORR/LOG ERROR OERI STANDBY FIXED_11.2.0.2 FIXED_12.1.0.0

Please note: The above is a summary description only. Actual symptoms can vary. Matching to any symptoms here does not confirm that you are encountering this problem. For questions about this bug please consult Oracle Support.


References
Bug:8895202 (This link will only work for PUBLISHED bugs)
Note:245840.1 Information on the sections in this article




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