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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，若搭建實時應(yīng)用日志的物理備庫，那么在主庫數(shù)據(jù)文件少量壞塊的情況下，可以利用ABCR技術(shù)快速修復(fù)壞塊
（一）
ABCR 功能是否開啟由隱含參數(shù) _auto_bmr 控制，默認(rèn)為 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同步狀態(tài)，可以看到當(dāng)前是一臺物理備庫
DGMGRL> show configuration Configuration - orcl Protection Mode:
MaxPerformance Databases: orcl - Primary database standby - Physical standby
database Fast-Start Failover: DISABLED Configuration Status: SUCCESS
（三）
配置下測試環(huán)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）
首先測試下在不開啟ABCR功能的情況下，壞塊是否可以自動修復(fù)
alter system set "_auto_bmr" = disabled;
搞破壞
dd if=/dev/zero of=/u01/app/oracle/oradata/orcl/users01.dbf bs=8192 seek=300
count=2 conv=notrunc
查詢報錯
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'
確認(rèn)壞塊的對象，并人為修復(fù)
sys@ORCL> select * from v$database_block_corruption; FILE# BLOCK# BLOCKS
CORRUPTION_CHANGE# CORRUPTIO ---------- ---------- ----------
------------------ --------- 4 300 2 0 ALL ZERO RMAN> blockrecover datafile 4
block 301; RMAN> blockrecover datafile 4 block 301;
（五）
開啟ABMR時又怎么樣呢？
alter system set "_auto_bmr" = enabled;
搞破壞
dd if=/dev/zero of=/u01/app/oracle/oradata/orcl/users01.dbf bs=8192 seek=400
count=2 conv=notrunc sys@ORCL> select * from v$database_block_corruption; FILE#
BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTIO ---------- ---------- ----------
------------------ --------- 4 400 2 0 ALL ZERO
查詢沒有報錯
alter system flush buffer_cache; select count(*) from baiyang.T_OBJS; COUNT(*)
---------- 84428
查看告警日志，自動修復(fù)壞塊
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)
數(shù)據(jù)庫塊的修復(fù)方式還有有多種，如RMAN blockrecover、RMAN
datafilerecover、DatabaseRecoveryAdvisor、DGswitchover等，ABCR無疑是最省心的一種，建議任何情況下都搭建ADG的主備架構(gòu)，避免故障被觸發(fā)概率。
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