RMAN是Oracle推出的官方备份还原工具。经过几个大版本的发展,RMAN已经支持多种备份介质和恢复策略的主要工具,也是业界普遍认可是Oracle备份还原官方策略。
Archivelog是Oracle备份还原策略的重要组成元素,不完全备份+连续的归档日志可以让我们将数据库恢复到发生故障点,实现数据的无损失恢复。但是,现实生活中archive log给没有经验的运维人员也带来了不少的问题,归档空间占满引起Hang住、瞬间归档日志过多生成引起问题等。一些前辈也在不断强调“归档模式不美好”。
在RMAN工作参数中,针对archive log,是可以设置专门的删除策略(Deletion)。在实践领域中,已经备份过或者确保安全传输的归档日志,其实就可以删除了,特别是在有限的Fast Recovery Area管理模式下。对于自动删除archive log的策略,比较常见的是applied to standby和shipped to standby,也就是Data Guard场景下。
本篇介绍简单的backed up参数使用情况,并通过一系列实验去研究该参数影响下Oracle和RMAN的工作行为特性。
1、基本参数和实验环境
笔者使用Oracle 11gR2进行测试,具体版本编号为11.2.0.4。
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 – Production
默认情况下,archivelog deletion policy参数为NONE。
RMAN> show all;
RMAN configuration parameters for database with db_unique_name XXXXDB are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
(篇幅原因,有省略……)
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
该参数常见的集中取值如下:
configure archivelog deletion policy to backed up 2 times to sbt;
configure archivelog deletion policy to backed up 1 times to device type disk;
configure archivelog deletion policy to applied on standby; --DG专用
configure archivelog deletion policy to shipped on standby; --DG专用
configure archivelog deletion policy clear;
研究archivelog行为最好的工具视图是v$archived_log。很多DBA喜欢从操作系统层面删除归档日志,但是这种方式是不会直接被Oracle控制文件认可,所以建议使用RMAN或者官方工具来做。
--已归档未删除日志
SQL> select count(*) from v$archived_log where archived='YES' and deleted='NO';
COUNT(*)
----------
13
2、第一轮备份测试实验
首先我们修改archivelog deletion policy参数,设置为“两次备份后即可以删除”。
RMAN> configure archivelog deletion policy to backed up 2 times to device type disk;
new RMAN configuration parameters:
CONFIGURE ARCHIVELOG DELETION POLICY TO BACKED UP 2 TIMES TO DISK;
new RMAN configuration parameters are successfully stored
手工备份数据库和归档日志,不进行删除动作。
RMAN> backup database plus archivelog;
Starting backup at 21-SEP-15
current log archived
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=16 device type=DISK
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=100 RECID=12 STAMP=890690423
input archived log thread=1 sequence=101 RECID=13 STAMP=890712061
input archived log thread=1 sequence=102 RECID=14 STAMP=890727732
input archived log thread=1 sequence=103 RECID=15 STAMP=890776815
input archived log thread=1 sequence=104 RECID=16 STAMP=890776833
input archived log thread=1 sequence=105 RECID=17 STAMP=890805616
input archived log thread=1 sequence=106 RECID=18 STAMP=890814181
input archived log thread=1 sequence=107 RECID=19 STAMP=890820201
input archived log thread=1 sequence=108 RECID=20 STAMP=890859629
input archived log thread=1 sequence=109 RECID=21 STAMP=890892046
input archived log thread=1 sequence=110 RECID=22 STAMP=890900632
input archived log thread=1 sequence=111 RECID=23 STAMP=890906655
input archived log thread=1 sequence=112 RECID=24 STAMP=890942416
input archived log thread=1 sequence=113 RECID=25 STAMP=890990204
channel ORA_DISK_1: starting piece 1 at 21-SEP-15
channel ORA_DISK_1: finished piece 1 at 21-SEP-15
piece handle=/u01/app/oracle/fast_recovery_area/XXXXDB/backupset/2015_09_21/o1_mf_annnn_TAG20150921T091644_bzypmwty_.bkp tag=TAG20150921T091644
(篇幅原因,省略部分……)
Finished Control File and SPFILE Autobackup at 21-SEP-15
此时,归档日志被备份,并且没有删除。
--多出来的两个是由于进行备份时候自动会有switch log
SQL> select count(*) from v$archived_log where archived='YES' and deleted='NO';
COUNT(*)
----------
15
下面进行第二次实验。
RMAN> backup database plus archivelog;
Starting backup at 21-SEP-15
current log archived
using channel ORA_DISK_1
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=100 RECID=12 STAMP=890690423
input archived log thread=1 sequence=101 RECID=13 STAMP=890712061
input archived log thread=1 sequence=102 RECID=14 STAMP=890727732
input archived log thread=1 sequence=103 RECID=15 STAMP=890776815
input archived log thread=1 sequence=104 RECID=16 STAMP=890776833
input archived log thread=1 sequence=105 RECID=17 STAMP=890805616
input archived log thread=1 sequence=106 RECID=18 STAMP=890814181
input archived log thread=1 sequence=107 RECID=19 STAMP=890820201
input archived log thread=1 sequence=108 RECID=20 STAMP=890859629
input archived log thread=1 sequence=109 RECID=21 STAMP=890892046
input archived log thread=1 sequence=110 RECID=22 STAMP=890900632
input archived log thread=1 sequence=111 RECID=23 STAMP=890906655
input archived log thread=1 sequence=112 RECID=24 STAMP=890942416
input archived log thread=1 sequence=113 RECID=25 STAMP=890990204
input archived log thread=1 sequence=114 RECID=26 STAMP=890990263
input archived log thread=1 sequence=115 RECID=27 STAMP=890990391
channel ORA_DISK_1: starting piece 1 at 21-SEP-15
channel ORA_DISK_1: finished piece 1 at 21-SEP-15
piece handle=/u01/app/oracle/fast_recovery_area/XXXXDB/backupset/2015_09_21/o1_mf_annnn_TAG20150921T091951_bzypsqj3_.bkp tag=TAG20150921T091951
(篇幅原因,有省略……)
Finished Control File and SPFILE Autobackup at 21-SEP-15