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小知识：什么叫做workaround？

2023-03-15 20:48  AlfredZhao  阅读(338)  评论(0)  编辑  收藏  举报

技术人当遇到具体问题，能给出的各种解决方案，有一种类型叫做workaround，翻译过来通常为“应变方法”、“变通方法”；
其实这种方式通常是没有找到根本的解决方案，但是为了快速恢复业务而采用的一种巧妙规避/跳过的方式。

举个具体的例子：我有测试需求要在主库创建一个新的PDB：

1.创建新的PDB

创建一个专门存放AWRDUMP的PDB

CREATE PLUGGABLE DATABASE awr
  ADMIN USER awr IDENTIFIED BY awr
  ROLES = (dba)
  DEFAULT TABLESPACE tbs_awr
    DATAFILE '/flash/oradata/DEMO/awr/awr01.dbf' SIZE 250M AUTOEXTEND ON maxsize 10G
  FILE_NAME_CONVERT = ('/flash/oradata/DEMO/pdbseed/',
                       '/flash/oradata/DEMO/awr/')
  STORAGE (MAXSIZE 2G)
  PATH_PREFIX = '/flash/oradata/DEMO/awr/';

主库创建成功没问题。

2.发现DG备库出现同步问题

发现备库没有同步，排查alert日志发现因为这个awr的目录不会自动创建，导致报错，最终引发MRP进程终止，详细告警日志如下：

2023-03-15T18:03:53.650192+08:00
Recovery of Online Redo Log: Thread 1 Group 11 Seq 446 Reading mem 0
  Mem# 0: +DATADG/DEMORAC/ONLINELOG/group_11.276.1127389115
PR00 (PID:11733): Media Recovery Waiting for T-1.S-447 (in transit)
2023-03-15T18:03:55.023213+08:00
Recovery of Online Redo Log: Thread 1 Group 13 Seq 447 Reading mem 0
  Mem# 0: +DATADG/DEMORAC/ONLINELOG/group_13.278.1127389119
2023-03-15T18:38:28.999341+08:00
Recovery created pluggable database AWR
Automatic Copy of Standby datafiles for create pdb failed with            error - 65169. Files need to be copied manually
2023-03-15T18:38:29.121847+08:00
Errors in file /u01/app/oracle/diag/rdbms/demorac/jydb1/trace/jydb1_pr00_11733.trc:
ORA-65169: error encountered while attempting to copy file +DATADG/DEMORAC/pdbseed/system01.dbf
ORA-19504: failed to create file "+DATADG/DEMORAC/awr/system01.dbf"
ORA-17502: ksfdcre:4 Failed to create file +DATADG/DEMORAC/awr/system01.dbf
ORA-15173: entry 'awr' does not exist in directory 'DEMORAC'
PR00 (PID:11733): MRP0: Background Media Recovery terminated with error 1274
2023-03-15T18:38:29.188919+08:00
Errors in file /u01/app/oracle/diag/rdbms/demorac/jydb1/trace/jydb1_pr00_11733.trc:
ORA-01274: cannot add data file that was originally created as '/flash/oradata/DEMO/awr/system01.dbf'
ORA-01565: error in identifying file '+DATADG/DEMORAC/awr/system01.dbf'
ORA-17503: ksfdopn:2 Failed to open file +DATADG/DEMORAC/awr/system01.dbf
ORA-15173: entry 'awr' does not exist in directory 'DEMORAC'
2023-03-15T18:38:29.195972+08:00
.... (PID:5407): Managed Standby Recovery not using Real Time Apply
2023-03-15T18:38:29.340321+08:00
Recovery interrupted!

IM on ADG: Start of Empty Journal

IM on ADG: End of Empty Journal
Recovered data files to a consistent state at change 23401386
2023-03-15T18:38:29.903857+08:00
Increasing priority of 2 RS
Reconfiguration started (old inc 6, new inc 8)
List of instances (total 2) :
 1 2
My inst 1
 Global Resource Directory frozen
 Communication channels reestablished
 Master broadcasted resource hash value bitmaps
 Non-local Process blocks cleaned out
2023-03-15T18:38:29.983551+08:00
 LMS 0: 0 GCS shadows cancelled, 0 closed, 0 Xw survived, skipped 0
2023-03-15T18:38:29.986436+08:00
 LMS 1: 0 GCS shadows cancelled, 0 closed, 0 Xw survived, skipped 0
 Set master node info
 Dwn-cvts replayed, VALBLKs dubious
 All grantable enqueues granted
Reconfiguration complete (total time 0.3 secs)
Decreasing priority of 2 RS
2023-03-15T18:38:30.492490+08:00
Stopping change tracking
2023-03-15T18:38:30.501521+08:00
Errors in file /u01/app/oracle/diag/rdbms/demorac/jydb1/trace/jydb1_pr00_11733.trc:
ORA-01274: cannot add data file that was originally created as '/flash/oradata/DEMO/awr/system01.dbf'
ORA-01565: error in identifying file '+DATADG/DEMORAC/awr/system01.dbf'
ORA-17503: ksfdopn:2 Failed to open file +DATADG/DEMORAC/awr/system01.dbf
ORA-15173: entry 'awr' does not exist in directory 'DEMORAC'
2023-03-15T18:38:30.524601+08:00
Background Media Recovery process shutdown (jydb1)

3.如何解决？

如果是找根本解决方案，那就是要研究为何无法自动创建成功，是否能够自动创建成功，具体的改进方案？
如果一时找不到方案，急于恢复同步，那其实手工创建这个目录，然后重新开启同步，就能快速解决，但这种解决方式就叫做workaround：

ASMCMD> pwd
+DATADG/DEMORAC
ASMCMD> mkdir AWR


SQL> recover managed standby database disconnect;
Media recovery complete.
SQL> set lines 180
SQL> col name for a22
SQL> col value for a22
SQL> select * from v$dataguard_stats;
SOURCE_DBID SOURCE_DB_ NAME		      VALUE		     UNIT			    TIME_COMPUTED		   DATUM_TIME			      CON_ID
----------- ---------- ---------------------- ---------------------- ------------------------------ ------------------------------ ------------------------------ ----------
	  0	       transport lag	      +00 00:00:00	     day(2) to second(0) interval   03/15/2023 20:23:51 	   03/15/2023 20:23:50			   0
	  0	       apply lag	      +00 00:00:00	     day(2) to second(0) interval   03/15/2023 20:23:51 	   03/15/2023 20:23:50			   0
	  0	       apply finish time      +00 00:00:00.000	     day(2) to second(3) interval   03/15/2023 20:23:51 						   0
	  0	       estimated startup time 18		     second			    03/15/2023 20:23:51 						   0

SQL> !ps -ef|grep mrp
oracle   27472     1  0 20:22 ?        00:00:00 ora_mrp0_jydb1
oracle   27677 27436  0 20:24 pts/2    00:00:00 /bin/bash -c ps -ef|grep mrp
oracle   27679 27677  0 20:24 pts/2    00:00:00 grep mrp

从alert日志也可以看到，快速解决了问题：

2023-03-15T20:22:38.685163+08:00
ALTER DATABASE RECOVER  managed standby database disconnect
2023-03-15T20:22:38.720205+08:00
Attempt to start background Managed Standby Recovery process (jydb1)
Starting background process MRP0
2023-03-15T20:22:38.745104+08:00
MRP0 started with pid=76, OS id=27472
2023-03-15T20:22:38.747543+08:00
Background Managed Standby Recovery process started (jydb1)
2023-03-15T20:22:43.778604+08:00
Starting single instance redo apply (SIRA)
 Started logmerger process
2023-03-15T20:22:43.859358+08:00

IM on ADG: Start of Empty Journal

IM on ADG: End of Empty Journal
2023-03-15T20:22:43.877044+08:00
.... (PID:5407): Managed Standby Recovery starting Real Time Apply
2023-03-15T20:22:43.940962+08:00
max_pdb is 5
2023-03-15T20:22:44.268320+08:00
Increasing priority of 2 RS
Reconfiguration started (old inc 8, new inc 10)
List of instances (total 2) :
 1 2
My inst 1
 Global Resource Directory frozen
 Communication channels reestablished
 Master broadcasted resource hash value bitmaps
 Non-local Process blocks cleaned out
2023-03-15T20:22:44.337010+08:00
 LMS 0: 0 GCS shadows cancelled, 0 closed, 0 Xw survived, skipped 0
2023-03-15T20:22:44.337017+08:00
 LMS 1: 0 GCS shadows cancelled, 0 closed, 0 Xw survived, skipped 0
 Set master node info
 Dwn-cvts replayed, VALBLKs dubious
 All grantable enqueues granted
Reconfiguration complete (total time 0.2 secs)
Decreasing priority of 2 RS
2023-03-15T20:22:45.062909+08:00
Parallel Media Recovery started with 4 slaves
2023-03-15T20:22:45.260072+08:00
Stopping change tracking
PR00 (PID:27481): Media Recovery Waiting for T-1.S-447 (in transit)
2023-03-15T20:22:45.456197+08:00
Recovery of Online Redo Log: Thread 1 Group 13 Seq 447 Reading mem 0
  Mem# 0: +DATADG/DEMORAC/ONLINELOG/group_13.278.1127389119
2023-03-15T20:22:45.548608+08:00
ALTER SYSTEM SET remote_listener='db01rac-scan:1521' SCOPE=MEMORY SID='jydb1';
2023-03-15T20:22:45.550060+08:00
ALTER SYSTEM SET listener_networks='' SCOPE=MEMORY SID='jydb1';
2023-03-15T20:22:45.765532+08:00
Completed: ALTER DATABASE RECOVER  managed standby database disconnect
2023-03-15T20:22:49.050096+08:00
Recovery copied files for tablespace SYSTEM
Recovery successfully copied file +DATADG/DEMORAC/awr/system01.dbf from +DATADG/DEMORAC/pdbseed/system01.dbf
AWR(5):Recovery created file +DATADG/DEMORAC/awr/system01.dbf
AWR(5):Successfully added datafile 21 to media recovery
AWR(5):Datafile #21: '+DATADG/DEMORAC/awr/system01.dbf'
2023-03-15T20:22:55.588650+08:00
Recovery copied files for tablespace SYSAUX
Recovery successfully copied file +DATADG/DEMORAC/awr/sysaux01.dbf from +DATADG/DEMORAC/pdbseed/sysaux01.dbf
AWR(5):Recovery created file +DATADG/DEMORAC/awr/sysaux01.dbf
AWR(5):Successfully added datafile 22 to media recovery
AWR(5):Datafile #22: '+DATADG/DEMORAC/awr/sysaux01.dbf'
2023-03-15T20:22:58.602144+08:00
Recovery copied files for tablespace UNDOTBS1
Recovery successfully copied file +DATADG/DEMORAC/awr/undotbs01.dbf from +DATADG/DEMORAC/pdbseed/undotbs01.dbf
AWR(5):Recovery created file +DATADG/DEMORAC/awr/undotbs01.dbf
AWR(5):Successfully added datafile 23 to media recovery
AWR(5):Datafile #23: '+DATADG/DEMORAC/awr/undotbs01.dbf'
2023-03-15T20:23:00.926349+08:00
AWR(5):Recovery created file +DATADG/DEMORAC/awr/awr01.dbf
AWR(5):Successfully added datafile 24 to media recovery
AWR(5):Datafile #24: '+DATADG/DEMORAC/awr/awr01.dbf'

最近高层给全员开会时提到要向前走一步，如果是落到技术岗位上，那就是要不满足workaround的解决方式，去找根本的解决方案。
实际情况当然要灵活变通，比如当生产环境需要快速恢复业务/功能时，可以使用各种workaround去应对确保快速恢复，但事后排查根本原因时还是要找到根本的解决方案。
所以，文中举的这个问题根本解决方案是？先留给大家一起思考吧。