Redo Log Dump

Redo logs keep the undo and redo information of every atomic database change operations. The changes are recorded as opcodes (operation codes), which are usually in the form of layer code.operation code format. For example, opcode 4.1 indicates block cleanout operation at transaction block layer.

Note, redo layers are not to be confused with Oracle ‚ s kernel layers. Redo layers are used only in conjunction with redo generation and redo logging.

Redo log dumps are normally requested by Oracle Support to analyze the data corruption (logical corruption) issues. If it is used intelligently it can be an auditing tool also. For example, if you would like to know the time and date of an extent allocated for a segment, you can dump the relevant opcodes for the extent allocation from the set of redo or archived log files and get the details that are not otherwise available in the data dictionary.

Syntax

The following methods show how to dump the redo log file contents.

Using ALTER SYSTEM

The following ALTER SYSTEM command can be used to dump redo logs. You can substitute the filters or options, depending on the requirement. If no filters are applied, the complete log file is dumped to the trace.

 alter session set max_dump_file_size = unlimited; 
 alter system dump logfile 'filename' 
 rba min <seqno> . <blkno> 
 rba max <seqno> . <blkno> 
 dba min <filno> . <blkno> 
 dba max <filno> . <blkno> 
 time min <ub4> 
 time max <ub4> 
 layer <word> 
 opcode <word> 
 scn min <scn> 
 scn max <scn> 
 alter system dump logfile '/u01/oradata/oraredo/redo_01a.rdo'; 

Controlling the Dump Information Using Levels

Not applicable . Redo dumping is based on various parameters such as, rba, dba, scn, or time. Not specifying any parameters will dump the entire redo log contents to the trace file. Archived redo logs also can be dumped using the preceeding ALTER SYSTEM command.