Oracle ADG 配置闪回导致报表查询延时！

前言

今天应用反馈有一套报表库查询有延时，几十分钟没有同步数据了，但是我检查 DG 同步状态之后发现一切正常，手动触发切换日志可以正常同步数据，但是无法实时查询主库的在线重做日志。

不是 DG 配置问题，不是 standby logfile 问题，不是网络问题，能是什么问题呢？

本文记录一下完整的分析过程以及解决方案。

检查 DG 状态

首先，先检查 DG 同步状态是否正常：

sql 复制代码

set linesize 2222 heading on wrap on
column dest_name format a20
column status format a8
column database_mode format a15
column recovery_mode format a35
column protection_mode format a25
column destination format a15
column archived_seq# format 999999999
column applied_seq# format 999999999
column error format a10
column srl format a5
column db_unique_name format a15
column gap_status format a10

SELECT inst_id, dest_name, status, database_mode, protection_mode,
       recovery_mode, gap_status, archived_seq#, applied_seq#, srl,
       db_unique_name, destination, error
FROM gv$archive_dest_status
WHERE status <> 'INACTIVE'
AND type = 'PHYSICAL';

   INST_ID DEST_NAME            STATUS   DATABASE_MODE   PROTECTION_MODE           RECOVERY_MODE                       GAP_STATUS ARCHIVED_SEQ# APPLIED_SEQ# SRL   DB_UNIQUE_NAME  DESTINATION     ERROR
---------- -------------------- -------- --------------- ------------------------- ----------------------------------- ---------- ------------- ------------ ----- --------------- --------------- ----------
         2 LOG_ARCHIVE_DEST_2   VALID    OPEN_READ-ONLY  MAXIMUM PERFORMANCE       MANAGED REAL TIME APPLY             NO GAP            123726       123725 YES   orcldg          orcldg
         1 LOG_ARCHIVE_DEST_2   VALID    OPEN_READ-ONLY  MAXIMUM PERFORMANCE       MANAGED REAL TIME APPLY             NO GAP            123726       123725 YES   orcldg          orcldg

检查备库同步进程：

sql 复制代码

set line2222 pages1000
select inst_id,pid,process,thread#,sequence#,status,delay_mins from gv$managed_standby;

   INST_ID        PID PROCESS      THREAD#  SEQUENCE# STATUS       DELAY_MINS
---------- ---------- --------- ---------- ---------- ------------ ----------
         1      10386 RFS                0          0 IDLE                  0
         1       3728 ARCH               2     123538 CLOSING               0
         1       3730 ARCH               0          0 CONNECTED             0
         1       3732 ARCH               2     123543 CLOSING               0
         1       3921 ARCH               2     123537 CLOSING               0
         1       4613 RFS                0          0 IDLE                  0
         1       4195 RFS                0          0 IDLE                  0
         1       4286 RFS                0          0 IDLE                  0
         1      10384 RFS                1     123728 IDLE                  0
         1      10381 RFS                2     123544 IDLE                  0
         1      10388 RFS                0          0 IDLE                  0
         1       4647 RFS                0          0 IDLE                  0
         1       5573 MRP0               1     123728 APPLYING_LOG          0

检查 DG 配置：

sql 复制代码

-- 主库
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_1                   string      LOCATION=+ARCH VALID_FOR=(ALL_
                                                 LOGFILES,ALL_ROLES) DB_UNIQUE_
                                                 NAME=ORCL
log_archive_dest_2                   string      service=orcldg LGWR ASYNC vali
                                                 d_for=(online_logfiles,primary
                                                 _role) db_unique_name=orcldg
-- 备库
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_1                   string
log_archive_dest_2                   string      service=orcl LGWR ASYNC valid_
                                                 for=(online_logfiles,primary_r
                                                 ole) db_unique_name=orcl

检查 standby logfile 状态：

sql 复制代码

   THREAD#     GROUP# MEMBER                                                                                               STATUS     ARC T2.BYTES/1024/1024
---------- ---------- ---------------------------------------------------------------------------------------------------- ---------- --- ------------------
         1          5 /u01/app/oracle/oradata/redostd05.log                                                                UNASSIGNED NO                 200
         1          6 /u01/app/oracle/oradata/redostd06.log                                                                UNASSIGNED NO                 200
         1          9 /u01/app/oracle/oradata/redostd09.log                                                                UNASSIGNED NO                 200
         2          7 /u01/app/oracle/oradata/redostd07.log                                                                UNASSIGNED NO                 200
         2          8 /u01/app/oracle/oradata/redostd08.log                                                                UNASSIGNED NO                 200
         2         10 /u01/app/oracle/oradata/redostd10.log                                                                UNASSIGNED NO                 200

通过以上查询可以发现，DG 配置以及同步都是正常的，应该不会出现无法实时查询的问题，那为什么会延时呢？

尝试在主库手动触发日志切换：

sql 复制代码

-- 主库执行
SQL> alter system archive log current;

发现数据可以正常同步过来，那就是说同步是没问题的。

检查 alert 日志

查看数据库 alert 日志看看是不是有报错：

bash 复制代码

## 在主库发现有报错
LNS: Attempting destination LOG_ARCHIVE_DEST_2 network reconnect (270)
LNS: Destination LOG_ARCHIVE_DEST_2 network reconnect abandoned
Error 270 for archive log file 2 to 'orcldg'
ORA-00270: error creating archive log

oerr 看一下报错的意思：

bash 复制代码

[oracle@orcl:/home/oracle]$ oerr ora 270
00270, 00000, "error creating archive log %s"
// *Cause:  An error was encountered when either creating or opening
//          the destination file for archiving.
// *Action: Check that the archive destination is valid and that there
//          is sufficient space on the destination device.

难道是 DG 的磁盘空间满了？

bash 复制代码

[oracle@orcldg:/]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_jxsemesdg01-lv_root
                      3.1T  2.6T  334G  89% /
tmpfs                  63G   72K   63G   1% /dev/shm
/dev/sda1             477M   79M  373M  18% /boot

磁盘空间还没满，那为什么无法创建归档？检查一下归档目录位置：

sql 复制代码

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     123726
Next log sequence to archive   0
Current log sequence           123727

没有设置归档目录，默认存放到闪回目录下，检查一下闪回配置：

sql 复制代码

SQL> show parameter db_recover

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      /u01/app/oracle/fast_recovery_
                                                 area
db_recovery_file_dest_size           big integer 100G

好的，破案了，闪回配置的空间上限设置了 100G，然后归档也是存放在闪回目录，当闪回目录达到上限之后，归档自然就无法写入了。

解决方案

解决方法也很简单，就是把归档日志从闪回目录独立出去：

bash 复制代码

[oracle@orcldg:/u01/app/oracle]$ mkdir archivelog
[oracle@orcldg:/u01/app/oracle]$ cd archivelog/
[oracle@orcldg:/u01/app/oracle/archivelog]$ pwd
/u01/app/oracle/archivelog

备库设置归档目录：

sql 复制代码

SQL> alter system set log_archive_dest_1='LOCATION=/u01/app/oracle/archivelog VALID_FOR=(ALL_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=orcldg';

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /u01/app/oracle/archivelog
Oldest online log sequence     123726
Next log sequence to archive   0
Current log sequence           123727

主库重新激活同步：

sql 复制代码

SQL> alter system set log_archive_dest_state_2=defer;

System altered.

SQL> alter system set log_archive_dest_state_2=enable;

System altered.

再从检查备库 standby logfile 状态：

sql 复制代码

SQL> select t2.thread#,t1.group#,t1.member,t2.STATUS,t2.ARCHIVED,t2.bytes/1024/1024 from v$logfile t1,v$standby_log t2 where t1.group#=t2.group# order by 1,2;

   THREAD#     GROUP# MEMBER                                                                                               STATUS     ARC T2.BYTES/1024/1024
---------- ---------- ---------------------------------------------------------------------------------------------------- ---------- --- ------------------
         1          5 /u01/app/oracle/oradata/redostd05.log                                                                UNASSIGNED NO                 200
         1          6 /u01/app/oracle/oradata/redostd06.log                                                                UNASSIGNED NO                 200
         1          9 /u01/app/oracle/oradata/redostd09.log                                                                UNASSIGNED NO                 200
         2          7 /u01/app/oracle/oradata/redostd07.log                                                                ACTIVE     YES                200
         2          8 /u01/app/oracle/oradata/redostd08.log                                                                UNASSIGNED NO                 200
         2         10 /u01/app/oracle/oradata/redostd10.log                                                                UNASSIGNED NO                 200

ADG 恢复实时查询，问题解决。

写在最后

一句话总结：闪回恢复区与归档日志共享空间时，必须做好空间规划和监控，否则会导致 DG 实时应用中断而难以察觉。生产环境建议将归档独立部署，避免空间竞争。