检查Data Guard 主库，发现log有如下信息：
Wed Oct 13 17:05:11 2010
RFS: Possible network disconnect with primary database
RFS: Destination database mount ID mismatch [0x4b1b0155:0x4b1b40c1]
RFS: client instance is standby database instead of primary
RFS: Not using real application clusters
查看备库，也有相关信息：
KUP-04021: field formatting error for field TEXT
KUP-04023: field start is after end of record
KUP-04101: record 989 rejected in file D:/oracle/admin/orcl/bdump/alert_orcl.log
KUP-04021: field formatting error for field TEXT
KUP-04023: field start is after end of record
KUP-04101: record 1038 rejected in file D:/oracle/admin/orcl/bdump/alert_orcl.log
Oracle 的解释：
Symptoms
Standby alert log reports "RFS: Possible network disconnect with primary database"
At the standby DB side I get this error every minute.
RFS: Possible network disconnect with primary database
Standby database ID mismatch [0xAAAA:0xBBBBB]
Archive log transfer/apply works O.K.
Cause
The (error) message may be triggered by another database that has log_archive_dest_2 pointing to standby instance of (error) message .
RFS process tries to communicate with the instance.
Solution
Check if you have DB with mismatched ID and its log_archive_dest_X parameter value.
If found one but not in primary/standby config, disable log_archive_dest_2 to the instance, ie
From the error message of "Standby database ID mismatch [0xAAAA:0xBBBBB]"
Convert the hex number of first argument, 0xAAAA to decimal value using calculator
Then search db with the dbid.
SQL> select dbid from v$database;
SQL> alter system set log_archive_dest_2_state=defer;
根据Oracle 的说法，是log_archive_dest_2参数的问题，检查了一下备库的参数，果然如此：
SQL> show parameter log_archive_dest_2
NAME TYPE VALUE
------------------------------------ ----------- --------------------
log_archive_dest_2 string service=orcl_1 （指向了主库）
SQL> alter system set log_archive_dest_2_state=defer;
系统已更改。
修改之后，再次检查主备的alert log。都没有了这种错误。
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