今天是2014-05-27，实在无聊顺便研究一下x$kccle的内容吧。如下全部是自己分析和实验结果，真实可靠。 1、如何获得v$log的底层表？我们可以通过autotrace完成查看如： SQL set autotrace trace expSQL set linesize 200SQL select * from v$log;Execution Pl
今天是2014-05-27，实在无聊顺便研究一下x$kccle的内容吧。如下全部是自己分析和实验结果，真实可靠。
1、如何获得v$log的底层表？我们可以通过autotrace完成查看如：
SQL> set autotrace trace exp
SQL> set linesize 200
SQL> select * from v$log;
Execution Plan
----------------------------------------------------------
Plan hash value: 2536105608
--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 197 | 0 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 1 | 197 | 0 (0)| 00:00:01 |
|* 2 | FIXED TABLE FULL | X$KCCLE | 1 | 148 | 0 (0)| 00:00:01 |
|* 3 | FIXED TABLE FIXED INDEX| X$KCCRT (ind:1) | 1 | 49 | 0 (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("LE"."LEDUP"<>0 AND "LE"."INST_ID"=USERENV('INSTANCE'))
3 - filter("RT"."INST_ID"=USERENV('INSTANCE') AND "LE"."LETHR"="RT"."RTNUM")
SQL>
可以知道当我们在查看v$log视图的时候，其实就是查看的x$kccle视图字段信息。查看该视图如下：
SQL> desc x$kccle Name Null? Type ----------------------------------------- -------- ---------------------------- ADDR RAW(8) INDX NUMBER INST_ID NUMBER 实例号 LENUM NUMBER 类似group_number LESIZ NUMBER logfile的size，是操作系统的blocks数目 LESEQ NUMBER v$log中的SEQUENCE# LEHWS NUMBER LEBSZ NUMBER block size（操作系统的块） LENAB NUMBER LEFLG NUMBER 表示日志的状态信息 LETHR NUMBER v$log中的THREAD# LELFF NUMBER 下一个logfile LELFB NUMBER 前一个logfile LELOS VARCHAR2(16) low scn类似v$log FIRST_CHANGE# LELOT VARCHAR2(20) low time类似v$log FIRST_TIME LENXS VARCHAR2(16) nex scn 类似v$log中下一个logfile的low FIRST_CHANGE#相同 LENXT VARCHAR2(20) nex time类似v$log中下一个logfile的low FIRST_TIME 相同 LEPVS VARCHAR2(16) prev scn, 与上一个logfile的low scn LEARF NUMBER archive link forward LEARB NUMBER archive link backward LEFNH NUMBER LEFNT NUMBER LEDUP NUMBER 等同于v$log中members SQL>
下面对比一下：
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIME
---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ------------
1 1 2944 104857600 1 YES INACTIVE 121424676 21-MAY-14
2 1 2945 104857600 1 NO CURRENT 121427428 21-MAY-14
3 1 2943 104857600 1 YES INACTIVE 121421889 21-MAY-14
SQL>
SQL> select inst_id,lenum,lesiz,leseq,lehws,lebsz,lebsz*lesiz log_size,lenab,leflg,lethr,lelff,lelfb,lelos from x$kccle;
INST_ID LENUM LESIZ LESEQ LEHWS LEBSZ LOG_SIZE LENAB LEFLG LETHR LELFF LELFB LELOS
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------------
1 1 204800 2944 2 512 104857600 190256 1 1 2 0 121424676
1 2 204800 2945 1 512 104857600 4294967295 8 1 3 1 121427428
1 3 204800 2943 2 512 104857600 190256 1 1 0 2 121421889
SQL>
SQL> select inst_id,lenum,leseq,lethr,lelot,lenxs,lenxt,lepvs,learf,learb,lefnh,lefnt,ledup from x$kccle;
INST_ID LENUM LESEQ LETHR LELOT LENXS LENXT LEPVS LEARF LEARB LEFNH LEFNT LEDUP
---------- ----- ----- ---------- -------------------- ---------------- -------------------- ---------------- ---------- ---------- ---------- ---------- ----------
1 1 2944 1 05/21/2014 11:26:42 121427428 05/21/2014 11:26:55 121421889 0 0 1 1 1
1 2 2945 1 05/21/2014 11:26:55 281474976710655 121424676 0 0 2 2 1
1 3 2943 1 05/21/2014 11:26:30 121424676 05/21/2014 11:26:42 121419052 0 0 3 3 1
SQL>
现在单独关注一下leflg字段，当该值为8说明是正在使用的logfile group：
dump出控制文件中的log file信息如下：
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 19 52428800 512 2 NO CURRENT 1013368 27-MAY-14 2.8147E+14
2 1 17 52428800 512 2 NO ACTIVE 1013348 27-MAY-14 1013365 27-MAY-14
3 1 18 52428800 512 2 NO ACTIVE 1013365 27-MAY-14 1013368 27-MAY-14
SQL> oradebug setmypid
Statement processed.
SQL> oradebug dump controlf 12
Statement processed.
注意：也可以使用alter system set events ‘immediate trace name controlf level 12';完成控制文件的dump操作：
LOG FILE RECORDS *************************************************************************** (size = 72, compat size = 72, section max = 16, section in-use = 3, last-recid= 17, old-recno = 0, last-recno = 0) (extent = 1, blkno = 10, numrecs = 16) LOG FILE #1: name #5: /u01/app/oracle/oradata/RHYS/onlinelog/o1_mf_1_9r1z70w0_.log name #6: /u01/app/oracle/fast_recovery_area/RHYS/onlinelog/o1_mf_1_9r1z70z2_.log Thread 1 redo log links: forward: 2 backward: 0 siz: 0x19000 seq: 0x00000013 hws: 0x1 bsz: 512 nab: 0xffffffff flg: 0x8 dup: 2 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.000f7675 Low scn: 0x0000.000f7678 05/27/2014 17:54:08 Next scn: 0xffff.ffffffff 01/01/1988 00:00:00 LOG FILE #2: name #3: /u01/app/oracle/oradata/RHYS/onlinelog/o1_mf_2_9r1z726s_.log name #4: /u01/app/oracle/fast_recovery_area/RHYS/onlinelog/o1_mf_2_9r1z7291_.log Thread 1 redo log links: forward: 3 backward: 1 siz: 0x19000 seq: 0x00000011 hws: 0x2 bsz: 512 nab: 0x14 flg: 0x0 dup: 2 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.000f75ec Low scn: 0x0000.000f7664 05/27/2014 17:54:01 Next scn: 0x0000.000f7675 05/27/2014 17:54:05 LOG FILE #3: name #1: /u01/app/oracle/oradata/RHYS/onlinelog/o1_mf_3_9r1z73jf_.log name #2: /u01/app/oracle/fast_recovery_area/RHYS/onlinelog/o1_mf_3_9r1z73lp_.log Thread 1 redo log links: forward: 0 backward: 2 siz: 0x19000 seq: 0x00000012 hws: 0x2 bsz: 512 nab: 0x4 flg: 0x0 dup: 2 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.000f7664 Low scn: 0x0000.000f7675 05/27/2014 17:54:05 Next scn: 0x0000.000f7678 05/27/2014 17:54:08
对应一下：
SQL> select inst_id,lenum,leseq,lethr,lelot,lenxs,lenxt,lepvs,learf,learb,lefnh,lefnt,ledup from x$kccle;
INST_ID LENUM LESEQ LETHR LELOT LENXS LENXT LEPVS LEARF LEARB LEFNH LEFNT LEDUP
---------- ----- ----- ---------- -------------------- ---------------- -------------------- ---------------- ---------- ---------- ---------- ---------- ----------
1 1 19 1 05/27/2014 17:54:08 281474976710655 1013365 0 0 5 6 2
1 2 17 1 05/27/2014 17:54:01 1013365 05/27/2014 17:54:05 1013228 0 0 3 4 2
1 3 18 1 05/27/2014 17:54:05 1013368 05/27/2014 17:54:08 1013348 0 0 1 2 2
SQL> select inst_id,lenum,lesiz,leseq,lehws,lebsz,lebsz*lesiz log_size,lenab,leflg,lethr,lelff,lelfb,lelos from x$kccle;
INST_ID LENUM LESIZ LESEQ LEHWS LEBSZ LOG_SIZE LENAB LEFLG LETHR LELFF LELFB LELOS
---------- ----- ---------- ----- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------------
1 1 102400 19 1 512 52428800 4294967295 8 1 2 0 1013368
1 2 102400 17 2 512 52428800 20 0 1 3 1 1013348
1 3 102400 18 2 512 52428800 4 0 1 0 2 1013365
SQL>
拿group3做一个分析：如下：
LOG FILE #3:（代表第三个group）
name #1: /u01/app/oracle/oradata/RHYS/onlinelog/o1_mf_3_9r1z73jf_.log（第一个日志文件）
name #2: /u01/app/oracle/fast_recovery_area/RHYS/onlinelog/o1_mf_3_9r1z73lp_.log（第二个日志文件）
Thread 1（线程1x$kccle.lethr） redo log links: forward: 0（对应x$kccle的LELFF为0) backward: 2(对应x$kccle的lelfb为2)
siz: 0x19000(对应x$kccle的lesiz转为10进制正好是102400）： seq: 0x00000012（转为10进制为18对应x$kccle的leseq）： hws: 0x2（对应x$kccle的lehws为2） bsz: 512（数据块对应x$kccle的lebsz）
nab: 0x4（对应lenab为4） flg: 0x0（对应x$kccle的leflg） dup: 2（对应x$kccle的ledup）
Archive links: fwrd: 0（前一个链表x$kccle的learf) back: 0 (对应x$kccle的learb）Prev scn: 0x0000.000f7664（转为10进制scn为1013348，对应lepvs)
Low scn: 0x0000.000f7675 05/27/2014 17:54:05(对应x$kccle的lelos）
Next scn: 0x0000.000f7678 05/27/2014 17:54:08（对应x$kccle的lenxt）
由此可知x$kccle正式抓取的是控制文件中的内容，这也是为什么数据块在mount状态下，可以查看v$log的原因了。
MySQL's Place: Databases and ProgrammingApr 13, 2025 am 12:18 AMMySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen
MySQL: From Small Businesses to Large EnterprisesApr 13, 2025 am 12:17 AMMySQL is suitable for small and large enterprises. 1) Small businesses can use MySQL for basic data management, such as storing customer information. 2) Large enterprises can use MySQL to process massive data and complex business logic to optimize query performance and transaction processing.
What are phantom reads and how does InnoDB prevent them (Next-Key Locking)?Apr 13, 2025 am 12:16 AMInnoDB effectively prevents phantom reading through Next-KeyLocking mechanism. 1) Next-KeyLocking combines row lock and gap lock to lock records and their gaps to prevent new records from being inserted. 2) In practical applications, by optimizing query and adjusting isolation levels, lock competition can be reduced and concurrency performance can be improved.
MySQL: Not a Programming Language, But...Apr 13, 2025 am 12:03 AMMySQL is not a programming language, but its query language SQL has the characteristics of a programming language: 1. SQL supports conditional judgment, loops and variable operations; 2. Through stored procedures, triggers and functions, users can perform complex logical operations in the database.
MySQL: An Introduction to the World's Most Popular DatabaseApr 12, 2025 am 12:18 AMMySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.
The Importance of MySQL: Data Storage and ManagementApr 12, 2025 am 12:18 AMMySQL is an open source relational database management system suitable for data storage, management, query and security. 1. It supports a variety of operating systems and is widely used in Web applications and other fields. 2. Through the client-server architecture and different storage engines, MySQL processes data efficiently. 3. Basic usage includes creating databases and tables, inserting, querying and updating data. 4. Advanced usage involves complex queries and stored procedures. 5. Common errors can be debugged through the EXPLAIN statement. 6. Performance optimization includes the rational use of indexes and optimized query statements.
Why Use MySQL? Benefits and AdvantagesApr 12, 2025 am 12:17 AMMySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.
Describe InnoDB locking mechanisms (shared locks, exclusive locks, intention locks, record locks, gap locks, next-key locks).Apr 12, 2025 am 12:16 AMInnoDB's lock mechanisms include shared locks, exclusive locks, intention locks, record locks, gap locks and next key locks. 1. Shared lock allows transactions to read data without preventing other transactions from reading. 2. Exclusive lock prevents other transactions from reading and modifying data. 3. Intention lock optimizes lock efficiency. 4. Record lock lock index record. 5. Gap lock locks index recording gap. 6. The next key lock is a combination of record lock and gap lock to ensure data consistency.
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
Atom editor mac version download
The most popular open source editor
SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.
PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
Dreamweaver CS6
Visual web development tools
mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),
