Oracle体系结构及备份（十五）——bg-lgwr

一 什么是LGWR进程

 

        LGWR写的条件：

        提交的时候

        达到三分之一满

        日志的大小达到1M

        每隔三秒

        在DBWn进程写之前

 

        The log writer process writes redo logentries to disk. Redo log entries are generated in the redo log buffer of thesystem global area (SGA). LGWR writes the redo log entries sequentially into aredo log file. If the database has a multiplexed redo log, then LGWR writes theredo log entries to a group of redo log files.

 

二 操作示例

[oracle@localhost 桌面]$ ps -ef | grep ora_ | grep lgw
oracle    6446     1  0 11:15 ?        00:00:00 ora_lgwr_orcl
[oracle@localhost 桌面]$ kill -9 6446
[oracle@localhost 桌面]$ ps -ef | grep ora_ | grep lgw
[oracle@localhost 桌面]$ ps -ef | grep ora_
oracle    6486  2720  0 11:17 pts/0    00:00:00 grep ora_
[oracle@localhost 桌面]$ sqlplus / as sysdba;

SQL*Plus: Release 10.2.0.1.0 - Production on Thu Jun 6 11:17:45 2013

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size		    1222192 bytes
Variable Size		  788531664 bytes
Database Buffers	   46137344 bytes
Redo Buffers		    2969600 bytes
Database mounted.
Database opened.
SQL> show parameter log_buff;

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
log_buffer			     integer	 2923520
SQL> exit;
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
[oracle@localhost 桌面]$ ps -ef | grep ora_ | grep lgw
oracle    6499     1  0 11:17 ?        00:00:00 ora_lgwr_orcl
[oracle@localhost 桌面]$ ps -ef | grep ora_
oracle    6491     1  0 11:17 ?        00:00:00 ora_pmon_orcl
oracle    6493     1  0 11:17 ?        00:00:00 ora_psp0_orcl
oracle    6495     1  0 11:17 ?        00:00:00 ora_mman_orcl
oracle    6497     1  0 11:17 ?        00:00:00 ora_dbw0_orcl
oracle    6499     1  0 11:17 ?        00:00:00 ora_lgwr_orcl
oracle    6501     1  0 11:17 ?        00:00:00 ora_ckpt_orcl
oracle    6503     1  0 11:17 ?        00:00:00 ora_smon_orcl
oracle    6505     1  0 11:17 ?        00:00:00 ora_reco_orcl
oracle    6507     1  0 11:17 ?        00:00:00 ora_cjq0_orcl
oracle    6509     1  0 11:17 ?        00:00:00 ora_mmon_orcl
oracle    6511     1  0 11:17 ?        00:00:00 ora_mmnl_orcl
oracle    6513     1  0 11:17 ?        00:00:00 ora_d000_orcl
oracle    6515     1  0 11:17 ?        00:00:00 ora_s000_orcl
oracle    6519     1  0 11:17 ?        00:00:00 ora_qmnc_orcl
oracle    6525     1  0 11:18 ?        00:00:00 ora_j000_orcl
oracle    6527     1  0 11:18 ?        00:00:00 ora_q000_orcl
oracle    6529     1  0 11:18 ?        00:00:00 ora_q001_orcl
oracle    6535  2720  0 11:18 pts/0    00:00:00 grep ora_

三 总结

 

        1.LGWR，将重做日志有序地写入重做日志文件中。

        2.LGWR写的条件：提交的时候、达到三分之一满、日志的大小达到1M、每隔三秒、在DBWn进程写之前。

        3. Log buffer：通过LGWR进程写入到logfile中。

        4.Linux中同样使用ps命令查看进程。

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  By Larry Wen

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