ORA-00600 [2662] ORA-600 [2662] “Block SCN is ahead of Current SCN”

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Format: ORA-600 [2662] [a] [b] [c] [d] [e]


versions 6.0 to 10.1


A data block SCN is ahead of the current SCN.
The ORA-600 [2662] occurs when an SCN is compared to the dependent SCN stored in a UGA variable.
If the SCN is less than the dependent SCN then we signal the ORA-600 [2662] internal error.

Arg [a] Current SCN WRAP
Arg [b] Current SCN BASE
Arg [c] dependent SCN WRAP
Arg [d] dependent SCN BASE
Arg [e] Where present this is the DBA where the dependent SCN came from.


File and IO buffer management for redo logs




There are different situations where ORA-600 [2662] can be raised.

It can be raised on startup or duing database operation.

If not using Parallel Server, check that 2 instances have not mounted the same database.
Check for SMON traces and have the alert.log and trace files ready to send to support.
Check the SCN difference [argument d]-[argument b].

If the SCNs in the error are very close, then try to shutdown and startup the instance several times.
In some situations, the SCN increment during startup may permit the database to open. Keep track of the number of times you attempted a If the Known Issues section below does not help in terms of identifying a solution, please submit the trace files and alert.log to Oracle Support Services for further analysis.
Known Issues:

NB Bug Fixed Description
4453449, OERI:3020 / corruption errors from multiple FLASHBACK DATABASE
5889016 Corruption / OERI during recovery
2899477, Minimise risk of a false OERI[2662]
2764106, False OERI[2662] possible on SELECT which can crash the instance
2216823 OERI [2662] reusing a TEMPFILE with a restored database
2054025, OERI:2662 possible on new TEMPORARY index block
P 647927, Digital Unix ONLY: OERI:2662 could occur under heavy load
851959 OERI:2662 possible from distributed OPS select


There were 2 forms of this error until 7.2.3:
Type I: 4/5 argument forms –
The SCN found on a block (dependent SCN) is ahead of the
current SCN. See below for this
Type II: 1 Argument (before 7.2.3 only):
Oracle is in the process of writing a block to a log file.
If the calculated block checksum is less than or equal to 1
(0 and 1 are reserved) ORA-600 [2662] is returned.
This is a problem generating an offline immediate log marker
Type I
a. Current SCN WRAP
b. Current SCN BASE
c. dependent SCN WRAP
d. dependent SCN BASE
e. Where present this is the DBA where the dependent SCN came from.
From kcrf.h:
If the SCN comes from the recent or current SCN then a dba
of zero is saved. If it comes from undo$ because the undo segment is
not available then the undo segment number is saved, which looks like
a block from file 0. If the SCN is for a media recovery redo (i.e.

block number == 0 in change vector), then the dba is for block 0
of the relevant datafile. If it is from another database for a
distributed transaction then dba is DBAINF(). If it comes from a TX
lock then the dba is really usn<<16+slot.
Type II
a. checksum -> log block checksum – zero if none (thread # in old format)
In addition to different basic types from above, there are different
situations where ORA-600 [2662] type I can be raised.
Getting started:
(1) is the error raised during normal database operations (i.e. when the
database is up) or during startup of the database?
(2) what is the SCN difference [d]-[b] ( subtract argument ‘b’ from arg ‘d’)?
(3) is there a fifth argument [e] ?
If so convert the dba to file# block#
Is it a data dictionary object? (file#=1)
If so find out object name with the help of reference dictionary
from second database
(4) What is the current SQL statement? (see trace)
Which table is refered to?
Does the table match the object you found in previous step?
Be careful at this point: there may be no relationship between DBA in [e]
and the real source of problem (blockdump).
Deeper analysis:
(1) investigate trace file:
this will be a user trace file normally but could be an smon trace too
(2) search for: ‘buffer’
(“buffer dba” in Oracle7 dumps, “buffer tsn” in Oracle8/Oracle9 dumps)
this will bring you to a blockdump which usually represents the
‘real’ source of OERI:2662
WARNING: There may be more than one buffer pinned to the process
so ensure you check out all pinned buffers.
-> does the blockdump match the dba from e.?
-> what kind of blockdump is it?
(a) rollback segment header
(b) datablock
(c) other
Check list and possible causes
If Parallel Server check both nodes are using the same lock manager
instance & point at the same control files.
Possible causes:
(1) doing an open resetlogs with _ALLOW_RESETLOGS_CORRUPTION enabled
(2) a hardware problem, like a faulty controller, resulting in a failed
write to the control file or the redo logs
(3) restoring parts of the database from backup and not doing the
appropriate recovery
(4) restoring a control file and not doing a RECOVER DATABASE USING BACKUP
(5) having _DISABLE_LOGGING set during crash recovery
(6) problems with the DLM in a parallel server environment
(7) a bug


(1) if the SCNs in the error are very close, attempting a startup several
times will bump up the dscn every time we open the database even if
open fails. The database will open when dscn=scn.
(2)You can bump the SCN either on open or while the database is open
using Event:ADJUST_SCN (see Note:30681.1).
Be aware that you should rebuild the database if you use this
Once this has occurred you would normally want to rebuild the
database via exp/rebuild/imp as there is no guarantee that some
other blocks are not ahead of time.
Note:30681.1 Details of the ADJUST_SCN Event
Note:1070079.6 Alter System Checkpoint
Possible Causes:
Note:41399.1 Forcing the database open with `_ALLOW_RESETLOGS_CORRUPTION`
Known Bugs:
Fixed In. Bug No. Description
7.1.5 BUG:229873
7.1.3 Bug:195115 Miscalculation of SCN on startup for distributed TX ? Bug:297197 Port specific Solaris OPS problem
7.3 Bug:336196 Port specific IBM SP AIX problem -> dlm issue Bug:851959 OERI:2662 possible from distributed OPS select
Not fixed Bug:2216823 OERI:2662 reported when reusing tempfile with restored DB Bug:2177050 OERI:729 space leak possible (with tags “define var info”/”oactoid info”)
can corrupt UGA and cause OERI:2662

ora-600 ora-600 ora-600 ora-600 ora-600 ora-600 ora-600
ora-600 ora-600 ora-600 ora-600 ora-600 ora-600 ora-600
2662 2662 2662 2662 2662 2662 2662 2662 2662
2662 2662 2662 2662 2662 2662 2662 2662 2662




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