2. The log gap report overview
To ensure the primary and standby databases are up to date, you can run the Log Gap Report using the following command from the primary database server:
Important: In the example below the line numbers indicated below on the left with "1. -->", "2. -->" etc, is used only for documentation purpose to help explain the report and is not included in the actual report
[oracle@dbv1 /usr/dbvisit/standby]$ ./dbvctl -d DEV -i
Dbvisit Standby Database Technology (8.0.08.18467) (pid 828)
dbvctl started on dbv1: Tue Jan 10 22:07:17 2017
Dbvisit Standby log gap report for DEV thread 1 at 201701102207:
1.--> Destination database on dbv2 is at sequence: 10.
2.--> Source database on dbv1 is at log sequence: 14.
3.--> Source database on dbv1 is at archived log sequence: 13.
4.--> Dbvisit Standby last transfer log sequence: 11.
5.--> Dbvisit Standby last transfer at: 2017-01-10 22:06:34.
6.--> Archive log gap for DEV: 3.
7.--> Transfer log gap for DEV: 2.
8.--> Standby database time lag (DAYS-HH:MI:SS): +1:06:24.
dbvctl ended on dbv1: Tue Jan 10 22:07:19 2017
The report line numbers are explained in more detail below:
- Line 1 – Destination database on dbv2 is at log sequence: 10.
Shows the last log sequence (10) that was applied to the standby database.
- Line 2 – Source database on dbv1 is at log sequence: 14.
Shows the current log sequence on the primary (14). This is the log sequence that is current - not yet archived.
- Line 3 – Source database on dbv1 is at archived log sequence: 13.
Shows the latest archive log sequence (13) available on the primary database.
- Line 4 – Dbvisit Standby last transfer log sequence: 11.
Shows the last archive log sequence (11) that was transferred to the standby server.
- Line 5 – Dbvisit Standby last transfer at 2017-01-10 22:06:34.
The timestamp (YYYYMMDDHH24MI) of the last transfer.
- Line 6 – Archive log gap for DEV: 3.
This is one the most important lines to look at. It shows the Archive Log Gap, which means how many archive logs still need to be applied to the standby database. In this example, the value is 3. This indicates that my standby database is 3 logs behind the primary. If this value is 0 it means all available Archive logs from the primary have been applied to the standby, and it is up to date. Before doing a Graceful Switchover operation it is important to make sure this value is 0, with the exception when RAC is used, then one of the instances may have a value of 1. To reduce this value, run Dbvisit Standby on the standby database.
- Line 7 – Transfer log gap for DEV: 2.
The second most important line to look at is the value for the Transfer Log Gap, and in this example, the value is 2. This value indicates the number of logs that still need to be transferred to the standby server. To resolve this gap you need to run Dbvisit Standby on the primary server again to ship the latest available logs.
- Line 8 - Standby database time lag (DAYS-HH:MI:SS): +1:06:24.
The time displayed here provides you with an indication of how far behind in “Time” the standby database is from the primary. This value is calculated by looking at the current SCN number on the standby database, compared to the SCN number on the primary database. These numbers are converted to timestamps and the difference is then displayed.