Database Software

Hi everyone,

I have an issue with one of the dataguard servers here.
Basically, looking at the v$managed_standby, it is still applying the latest archived log sequence.
However when I checked for unapplied archived log from v$archived_log, I found at least 1 sequence# which was quite old (around a few days old) not applied.
my query to check this is:

SELECT sequence# from v$archived_log where applied = 'NO';

result:

SEQUENCE#
---------
    40154
    40546

with a different query I found an interesting result

select sequence#, recid, stamp, status, applied from v$archived_log where sequence# in (40154, 40546);

result:

SEQUENCE#      RECID      STAMP S APP
--------- ---------- ---------- - ---
    40154       8093  777156019 D NO
    40154       8095  777156053 D YES
    40546       8486  777673729 D NO
    40546       8487  777673734 D YES

At the time I ran this query, the v$managed_standby are as follow:

select process, status, sequence# from v$managed_standby;

result:

PROCESS   STATUS        SEQUENCE#
--------- ------------ ----------
ARCH      CLOSING           40562
ARCH      CLOSING           40557
MRP0      APPLYING_LOG      40563
RFS       IDLE                  0
RFS       IDLE              40563

A simple solution to get those un-applied archived log to be applied is to restart the standby database instance.
Another finding from the production database:

select recid, stamp, sequence#, creator, registrar, standby_dest from v$archived_log where sequence# in (40154, 40546);

result:

 RECID      STAMP  SEQUENCE# CREATOR REGISTR STA
------ ---------- ---------- ------- ------- ---
 45446  777156011      40154 ARCH    ARCH    NO
 45447  777156017      40154 LGWR    LGWR    YES
 45450  777156051      40154 ARCH    ARCH    YES
 46231  777673709      40546 ARCH    ARCH    NO
 46232  777673728      40546 LGWR    LGWR    YES
 46233  777673733      40546 ARCH    ARCH    YES

The question is of course, why is this happening?
Can this be prevented?

Thank you,
Adhika