Oracle Dataguard 下块自动修复技术 - 好文

Oracle Active Data Guard and Automatic Block Repair

Starting in Oracle Database 11g Release 2 (11.2), the primary database
automatically attempts to repair the corrupted block in real time by fetching a
good version of the same block from a physical standby database. This
capability is referred to as automatic block repair, and it allows corrupt data
blocks to be automatically repaired as soon as the corruption is detected.
Automatic block repair reduces the amount of time that data is inaccessible due
to block corruption. It also reduces block recovery time by using up-to-date
good blocks in real-time, as opposed to retrieving blocks from disk or tape
backups, or from Flashback logs.

在Oracle11gr2版本之后，若搭建实时应用日志的物理备库，那么在主库数据文件少量坏块的情况下，可以利用ABCR技术快速修复坏块

（一）
ABCR 功能是否开启由隐含参数 _auto_bmr 控制，默认为 ENABLE
select * from v$version; BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production CORE 11.2.0.4.0 Production TNS for
Linux: Version 11.2.0.4.0 - Production NLSRTL Version 11.2.0.4.0 - Production
col NAME for a30 col VALUE for a30 col describ for a40 SELECT x.ksppinm NAME,
y.ksppstvl VALUE, x.ksppdesc describ FROM x$ksppi x,x$ksppcv y WHERE x.inst_id
= USERENV ('Instance') AND y.inst_id = USERENV ('Instance') AND x.indx = y.indx
AND x.ksppinm LIKE '%_auto_bmr%'; NAME VALUE DESCRIB
------------------------------ ------------------------------
---------------------------------------- _auto_bmr ENABLE enable/disable Auto
BMR _auto_bmr_req_timeout 60 Auto BMR Requester Timeout
_auto_bmr_sess_threshold 30 Auto BMR Request Session Threshold
_auto_bmr_pub_timeout 10 Auto BMR Publish Timeout _auto_bmr_fc_time 60 Auto BMR
Flood Control Time _auto_bmr_bg_time 3600 Auto BMR Process Run Time
_auto_bmr_sys_threshold 100 Auto BMR Request System Threshold
_auto_bmr_max_rowno 1024 x$krbabrstat Max number of rows
（二）
DG同步状态，可以看到当前是一台物理备库
DGMGRL> show configuration Configuration - orcl Protection Mode:
MaxPerformance Databases: orcl - Primary database standby - Physical standby
database Fast-Start Failover: DISABLED Configuration Status: SUCCESS
（三）
配置下测试环境
create table T_OBJS as select * from all_objects ; create index
baiyang.idx_name on baiyang.T_OBJS(OBJECT_NAME); select
segment_name,header_file , header_block,blocks from dba_segments where OWNER
='BAIYANG' and segment_name ='T_OBJS'; OWNER SEGMENT_NAME HEADER_FILE
HEADER_BLOCK BLOCKS ------------------------------ -----------------
----------- ------------ ---------- SYS T_OBJS 4 300 1280
（四）
首先测试下在不开启ABCR功能的情况下，坏块是否可以自动修复
alter system set "_auto_bmr" = disabled;
搞破坏
dd if=/dev/zero of=/u01/app/oracle/oradata/orcl/users01.dbf bs=8192 seek=300
count=2 conv=notrunc
查询报错
alter system flush buffer_cache; select count(*) from baiyang.T_OBJS; > select
count(*) from baiyang.T_OBJS > * > ERROR at line 1: > ORA-01578: ORACLE data
block corrupted (file # 4, block # 300) > ORA-01110: data file 4:
'/u01/app/oracle/oradata/orcl/users01.dbf'
确认坏块的对象，并人为修复
sys@ORCL> select * from v$database_block_corruption; FILE# BLOCK# BLOCKS
CORRUPTION_CHANGE# CORRUPTIO ---------- ---------- ----------
------------------ --------- 4 300 2 0 ALL ZERO RMAN> blockrecover datafile 4
block 301; RMAN> blockrecover datafile 4 block 301;
（五）
开启ABMR时又怎么样呢？
alter system set "_auto_bmr" = enabled;
搞破坏
dd if=/dev/zero of=/u01/app/oracle/oradata/orcl/users01.dbf bs=8192 seek=400
count=2 conv=notrunc sys@ORCL> select * from v$database_block_corruption; FILE#
BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTIO ---------- ---------- ----------
------------------ --------- 4 400 2 0 ALL ZERO
查询没有报错
alter system flush buffer_cache; select count(*) from baiyang.T_OBJS; COUNT(*)
---------- 84428
查看告警日志，自动修复坏块
Wed Dec 05 15:55:59 2018 Automatic block media recovery successful for (file#
4, block# 401) Automatic block media recovery successful for (file# 4, block#
402)
数据库块的修复方式还有有多种，如RMAN blockrecover、RMAN
datafilerecover、DatabaseRecoveryAdvisor、DGswitchover等，ABCR无疑是最省心的一种，建议任何情况下都搭建ADG的主备架构，避免故障被触发概率。

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