How To Determine The Cause Of Lots Of Redo Generation Using LogMiner (Doc ID 300395.1)

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How To Determine The Cause Of Lots Of Redo Generation Using LogMiner (Doc ID 300395.1)

APPLIES TO:

Oracle Database - Enterprise Edition - Version 8.1.7.4 to 10.2.0.5 [Release 8.1.7 to 10.2]
Oracle Database - Enterprise Edition - Version 11.2.0.1 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Information in this document applies to any platform.
NOTE: In the images and/or the document content below, the user information and data used represents fictitious data. Any similarity to actual persons, living or dead, is purely coincidental and not intended in any manner.

GOAL

This article provides guidelines DBAs can use to determine which OPERATION codes are generating lots of redo information.

本文提供了DBA可用来确定哪些 OPERATION 代码正在生成大量 redo 的准则。

This article is intended for DBAs. The article assumes the reader is familiar with LogMiner and has basic skills in mining redo logs.

本文适用于DBA。 本文假定读者熟悉 LogMiner，并且具有挖掘redo日志的基本技能。

SOLUTION

--- How to determine the cause of lots of redo generation using LogMiner ---

--- 如何使用 LogMiner 确定产生大量 redo 的原因 ---

Using OPERATION Codes to Understand Redo Information  使用 OPERATION 了解 Redo 信息

There are multiple operation codes which can generate the redo information, using following guide lines you can identify the operation codes which are causing the high redo generation and you need to take an appropriate action on it to reduce the high redo generation.

有多种操作代码可以生成redo信息，使用以下指南，您可以识别导致高redo生成的操作代码，并且需要对其采取适当的措施以减少高redo生成。

NOTE:
Redo records are not all equally sized. So remember that just because certain statements show up a lot in the LogMiner output, this does not guarantee that you have found the area of functionality generating the excessive redo.
Redo记录的大小并不均等。 因此请记住，仅因为某些语句在LogMiner输出中显示很多，这并不能保证您已经找到了产生过多redo的功能区域。


What are these OPERATION codes ?  这些操作代码是什么？

  • INSERT / UPDATE / DELETE -- Operations are performed on SYS objects are also considered as an Internal Operations. 对SYS对象执行的操作也被视为内部操作。
  • COMMIT -- This is also "Internal" operation, you will get line "commit;" in the column sql_redo.  这也是“内部”操作，您将 在sql_redo列中 获得“ commit;”行 。
  • START -- This is also "Internal" operation, you will get line "set transaction read write;" in sql_redo INTERNAL -- Dictionary updates  这也是“内部”操作，您将在 sql_redo INTERNAL -- Dictionary updates获得"set transaction read write;"
  • SELECT_FOR_UPDATE - This is also an Internal operation and oracle generates the redo information for "select" statements which has "for update" clause. 这也是一个内部操作，并且oracle为具有 "for update" 子句的 "select" 语句生成redo信息。

In general INTERNAL operations are not relevant, so to query the relevant data, use "seg_owner=‘ in the "where" clause.

通常，INTERNAL操作无关紧要，因此要查询相关数据，请在"where" 子句中使用"seg_owner=‘ 。

Examples:

How to extract relevant information from the view v$logmnr_contents?

如何从视图 v$logmnr_contents 中提取相关信息

1. This SQL lists operations performed by user SCOTT  该SQL列出了用户SCOTT执行的操作

SQL> select distinct operation,username,seg_owner from v$logmnr_contents where seg_owner=‘SCOTT‘;

OPERATION USERNAME SEG_OWNER
-------------------------- ------------------------- ---------------------
DDL SCOTT SCOTT
DELETE SCOTT SCOTT
INSERT SCOTT SCOTT
UPDATE SCOTT SCOTT

2. This SQL lists the undo and redo associated with operations that user SCOTT performed

此SQL列出与用户SCOTT执行的操作相关的undo和redo

SQL> select seg_owner,operation,sql_redo,sql_undo from v$logmnr_contents where SEG_owner=‘SCOTT‘;

SCOTT DDL
create table LM1 (c1 number, c2 varchar2(10));

SCOTT INSERT
insert into "SCOTT"."LM1"("C1","C2") values (‘101‘,‘AAAA‘);
delete from "SCOTT"."LM1" where "C1" = ‘101‘ and "C2" = ‘AAAA‘
and ROWID = ‘AAAHfBAABAAAMUqAAA‘;

SCOTT UPDATE update "SCOTT"."LM1" set "C2" = ‘YYY‘
where "C2" = ‘EEE‘ and ROWID = ‘AAAHfBAABAAAMUqAAE‘;
update "SCOTT"."LM1" set "C2" = ‘EEE‘ where "C2" = ‘YYY‘
and ROWID = ‘AAAHfBAABAAAMUqAAE‘;

INSERT / UPDATE / DELETE -- Operations are performed on SYS objects are also considered as an Internal Operations. 对SYS对象执行的操作也被视为内部操作

3. This SQL lists undo and redo generated for UPDATE statements issues by user SCOTT  此SQL列出了用户SCOTT为UPDATE语句问题生成的undo和redo

SQL> select username, seg_owner,operation,sql_redo,sql_undo from v$logmnr_contents where operation =‘UPDATE‘ and USERNAME=‘SCOTT‘;

UNAME SEG_OW OPERATION SQL_REDO SQL_UNDO
---------- ---------- ------------ -----------------------------------
SCOTT SYS UPDATE update "SYS"."OBJ$" set "OBJ#" = ‘1‘..... update ....
SCOTT SYS UPDATE update "SYS"."TSQ$" set "GRANTO..... update .......
SCOTT SYS UPDATE update "SYS"."SEG$" set "TYPE#" = ‘5‘.. update......

As per above result user SCOTT has updated SYS objects so, if you query on USERNAME, you may get incorrect result. So, better to query v$logmnr_contents on SEG_OWNER.
根据上述结果，用户SCOTT已更新了SYS对象，因此，如果您在USERNAME上进行查询，则可能会得到错误的结果。因此，最好在SEG_OWNER上查询 v$logmnr_contents。

4. Identifying Operation Counts 识别操作计数

Run the following query to see the OPERATION code row count from v$logmnr_contents, to understand which OPERATION code has generated lots of redo information.

运行以下查询以查看 v$logmnr_contents 中的 OPERATION 代码行计数，以了解哪个 OPERATION 代码已生成大量redo信息。

SQL> select operation,count(*) from v$logmnr_contents group by operation;

OPERATION COUNT(*)
-------------------- ----------
COMMIT 22236
DDL 2
DELETE 1
INSERT 11
INTERNAL 11
SELECT_FOR_UPDATE 32487
START 22236
UPDATE 480

8 rows selected

5. Identifying User Counts  识别用户数

Run the following query to check user activity and operation counts:  运行以下查询以检查用户活动和操作计数

SQL> select seg_owner,operation,count(*) from v$logmnr_contents group by seg_owner,operation;

SEG_OWNER OPERATION COUNT(*)
-------------------- ---------------- ---------
SCOTT COMMIT  22236
SCOTT DDL 2
SCOTT DELETE 1
...
BILLY COMMIT 12899
BILLY DDL 5
BILLY DELETE 2
...

 

NOTE: 
Be aware of next known issue:  请注意下一个已知问题

If you are not using "select for update" statements often in your application and yet find a high operation count for operation code "SELECT_FOR_UPDATE" then you might be hitting a known issue.

如果您不经常在应用程序中使用 "select for update" 语句，却发现操作代码 "SELECT_FOR_UPDATE" 的操作计数很高，那么您可能遇到了一个已知问题。

To confirm this check whether SQL_REDO shows select,update statements on AQ$_QUEUE_TABLE_AFFINITIES and AQ$_QUEUE_TABLES.

要确认此检查，SQL_REDO 是否在 AQ$_QUEUE_TABLE_AFFINITIES and AQ$_QUEUE_TABLES 上显示 select,update 语句。

If you see these selects and updates, then check the value of the Init.ora parameter AQ_TM_PROCESSES.  The default value is AQ_TM_PROCESSES = 0 meaning that the queue monitor is not created.

如果看到这些 selects and updates，请检查Init.ora参数AQ_TM_PROCESSES的值。 缺省值为AQ_TM_PROCESSES = 0表示未创建队列监视器。

If you are not using Advanced Queuing, then set AQ_TM_PROCESSES back to zero to avoid lots of redo generation on objects AQ$_QUEUE_TABLE_AFFINITIES and AQ$_QUEUE_TABLES.

如果不使用高级队列，则将AQ_TM_PROCESSES设置回零，以避免在对象 AQ$_QUEUE_TABLE_AFFINITIES and AQ$_QUEUE_TABLES 上产生大量redo。

REFERENCES

NOTE:291686.1 - LogMiner Utility Release 8i - 11g

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