dump日誌檔案的內容的研究（看別人的）

分享metalink上的doc
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本文介紹如何dump online的日誌檔案頭部資訊（也包括歸檔）
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. （在一些診斷時，需要dump redo log file）

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.
alter session用於dump 日誌頭而‘system dump logfile' 用於dump 日誌內容。This command requires 'ALTER SYSTEM' system privilege（需要 'ALTER SYSTEM' 系統許可權）. The database can be in mount, nomount or open state when the command is issued（可以是nomount狀態）. 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（只要作業系統一樣，也可以dump其他資料庫的dump檔案）.

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) --基於dba
2. To dump records based on RBA (Redo Block Address) --基於rda
3. To dump records based on time --基於時間
4. To dump records based on layer and opcode --基於？？
5. Dump the file header information --dump頭部資訊
6. Dump an entire log file: --dump全部日誌檔案
1. To dump records based on DBA (Data Block Address) --基於dba
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This will dump all redo records for the range of data blocks specified for a given file # and block # range. 指定檔案號和block範圍即可。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.

2. To dump records based on RBA (Redo Block Address)
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This will dump all redo records for the range of redo addresses specified for the given sequence number and block number.
指定scn號和塊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 time.
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Using this option will cause redo records created within the time range specified to be dumped to the trace file.
指定時間範圍。From sqldba or svrmgr, issue the following command:
ALTER SYSTEM DUMP LOGFILE 'filename'
TIME MIN value
TIME MAX value;

Example:
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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

4. To dump records based on layer and opcode.
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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:
用於dump特定重做記錄的所有日誌記錄。比如由sysdba執行的所有刪掉的行layer，與opcode應該是oracle自身的程式碼了。
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;

5. Dump the file header information:dump online的頭部資訊。
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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';

6. Dump an entire log file:指定log的路徑即可，可以是其他的資料庫的
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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';

由上面的思路就可以理解為什麼lgminer可以挖掘日誌了。

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