How to Dump Redo Log File Information

PURPOSE
This article explain how to obtain a dump of the header information in the
online redo log file(s), as well as obtaining selected information from the
online or archived redo log files.

SCOPE & APPLICATION
Informational

You are working with Oracle Technical Support. As part of the diagnostic
process, you have been asked to take a dump of the redo log files. The
information in the logs is often used to help diagnose corruption issues.

The following commands will be used in this process:

1. The 'alter session' command is used to dump redo headers.

2. Use the 'alter system dump logfile' to dump log file contents.

This command requires 'ALTER SYSTEM' system privilege. The database can be in
mount, nomount or open state when the command is issued. An online log file
or an archived log file can be dumped. It is even possible to dump a
file from another database, as long as the operating systems are the same.

Output from the command is put into the session's trace file.

The following ways of dumping a redo log file are covered:

1. To dump records based in DBA (Data Block Address)
2. To dump records based on RBA (Redo Block Address)
3. To dump records based on SCN
4. To dump records based on time
5. To dump records based on layer and opcode
6. Dump the file header information
7. Dump an entire log file:


1. To dump records based on DBA (Data Block Address)
--------------------------------------------------

This will dump all redo records for the range of data
blocks specified for a given file # and block # range.

From sqldba or svrmgr, issue the following command:

ALTER SYSTEM DUMP LOGFILE 'filename'
DBA MIN fileno . blockno
DBA MAX fileno . blockno;

Example:
========
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
DBA MIN 5 . 31125
DBA MAX 5 . 31150;

This will cause all the changes to the specified range of data blocks to be
dumped to the trace file. In the example given, all redo records for file #5,
blocks 31125 thru 31150 are dumped.

Note
====
For 10g:
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
DBA MIN 5 . 31125 DBA MAX 5 . 31150;

will raise:
ORA-01963: Must specify a block number

In 10g we need to skip the dot '.' while doing the redo dumps
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
DBA MIN 5 31125 DBA MAX 5 31150;


2. To dump records based on RBA (Redo Block Address)
-------------------------------------------------

This will dump all redo records for the range of redo
addresses specified for the given sequence number and block number.

Syntax:
ALTER SYSTEM DUMP LOGFILE 'filename'
RBA MIN seqno . blockno
RBA MAX seqno . blockno;

Example:
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
RBA MIN 2050 . 13255
RBA MAX 2255 . 15555;

3. To dump records based on SCN
----------------------------

Using this option will cause redo records owning changes within the SCN range
specified to be dumped to the trace file.

ALTER SYSTEM DUMP LOGFILE 'filename'
SCN MIN minscn
SCN MAX maxscn;

Example:
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
SCN MIN 103243
SCN MAX 103294;

If the purpose is to check the dumpfile you can rather do the following,
SQL> ALTER SYSTEM DUMP LOGFILE 'filename' SCN MIN 1 SCN MAX 1;

If the above completes sucessfully it ensures no issues with the archivelog.


4. To dump records based on time.
------------------------------

Using this option will cause redo records created within the time range
specified to be dumped to the trace file.

From sqldba or svrmgr, issue the following command:

ALTER SYSTEM DUMP LOGFILE 'filename'
TIME MIN value
TIME MAX value;

Example:
========
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
TIME MIN 299425687
TIME MAX 299458800;


Please Note: the time value is given in REDO DUMP TIME



5. To dump records based on layer and opcode.
------------------------------------------

LAYER and OPCODE are used to dump all log records for a particular type of
redo record, such as all dropped row pieces.

From sqldba or svrmgr, issue the following command:

ALTER SYSTEM DUMP LOGFILE 'filename'
LAYER value
OPCODE value;

Example:
========
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf'
LAYER 11
OPCODE 3;

6. Dump the file header information:
---------------------------------

This will dump file header information for every
online redo log file.

From sqldba or svrmgr, issue the following command:

alter session set events 'immediate trace name redohdr level 10';


7. Dump an entire log file:
------------------------

From sqldba or svrmgr, issue the following command:

ALTER SYSTEM DUMP LOGFILE 'filename';

Please note:
Fully qualify the filename, and include the single quotes.


Example:
========
ALTER SYSTEM DUMP LOGFILE 'u01/oracle/V7323/dbs/arch1_76.dbf';

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