Querying Data Guard Apply Lag

Onur ARDAHANLI

3 years ago

In today’s article we will cover Querying Data Guard Apply Lag.

We can find out if there is an Apply Lag by querying the view below.

SQL> set linesize 9000
SQL> col name format a10
SQL> SELECT * FROM V$STANDBY_EVENT_HISTOGRAM WHERE NAME = 'apply lag' AND COUNT > 0;

NAME             TIME UNIT                  COUNT LAST_TIME_UPDATED
---------- ---------- ---------------- ---------- --------------------
apply lag           0 seconds                1953 01/04/2017 09:53:09
apply lag           1 seconds                  15 01/04/2017 09:50:33
apply lag           2 seconds                   2 01/04/2017 09:36:53
apply lag           3 seconds                   1 01/04/2017 09:30:03

SQL> set linesize 9000

SQL> col name format a10

SQL> SELECT * FROM V$STANDBY_EVENT_HISTOGRAM WHERE NAME = 'apply lag' AND COUNT > 0;

NAME TIME UNIT COUNT LAST_TIME_UPDATED

---------- ---------- ---------------- ---------- --------------------

apply lag 0 seconds 1953 01/04/2017 09:53:09

apply lag 1 seconds 15 01/04/2017 09:50:33

apply lag 2 seconds 2 01/04/2017 09:36:53

apply lag 3 seconds 1 01/04/2017 09:30:03

From here it can be said that I have almost never experienced LAG.

If the highest number was 3-4-5 seconds instead of 0 seconds,

then I would have to work on whether this LAG was caused by CPU,

Network latency or Bandwith insufficiency.