Data Guard standby redo logs are worth a few comments. The misconception that there have to be the exact same number of standby redo logs as there are primary redo logs seems to come up often. In fact, the size has to be the same, but the standby should always have at least one more standby redo log group than the primary does. As well, if you are using threads/RAC on the primary, then you need to have one extra standby redo log group for each primary thread.
For example, a RAC database with three threads and 3 log groups in each thread would have 9 redo logs. A physical standby hanging off this primary database would then need to have a minimum of 12 standby redo logs. A logical standby would as well, but could be given even more standby redo logs to help with realtime log apply.
If you experience a large load/throughput on your primary database, and you do not have enough standby redo logs, you may run into this error:
RFS[89]: No standby redo logfiles of size 203806 blocks available
This is not to be confused with the error received when there is no standby redo log that matches the primary redo log’s size.
This section of the data guard documentation explains how to configure standby redo logs.
To see your standby redo logs, you use a special v$ view, v$standby_log. The only thing about this view to note is that “UNASSIGNED” means the same thing as “INACTIVE” does in the v$log view of normal redo logs.
Recently due to log file switch contention, I had to increase the size and number of the primary’s redo logs, which then meant doing the same to the standby logs. Since they are 10g logical standbys, they are open and also have their own redo logs. Those logs did not have to be modified.
To make primary redo log changes:
-- prod and standbys: set STANDBY_FILE_MANAGEMENT to MANUAL so file changes
-- are not transferred to standbys
alter system set STANDBY_FILE_MANAGEMENT=MANUAL scope=both;
-- standbys: stop log apply
ALTER DATABASE STOP LOGICAL STANDBY APPLY;
-- add new redo groups/logs - first a set of new ones,
-- then log switch until the database
-- is using the new ones, then drop the old groups and
-- replace them with the new size/naming
-- and the old group number
alter database add logfile group 4 ('/u03/oradata/MYDB/redo04.log') size 512M;
-- repeat until the new logs are active/current and the old ones are not
alter system switch logfile;
-- then:
alter system checkpoint;
select * from v$log;
-- can't drop a logfile group until it is archived
alter system archive log group X;
-- drop the old groups
alter database drop logfile group 1;
-- on the file system:
## clean up the old files
mv /u03/oradata/MYDB/redo101.log /u03/oradata/MYDB/old
alter database add logfile group 1 ('/u03/oradata/MYDB/redo01.log') size 512M;
---------------------------------------------------------------------
-- logical standbys - run on each - run on standby db unless noted
---------------------------------------------------------------------
-- stop log apply again to be sure
ALTER DATABASE STOP LOGICAL STANDBY APPLY;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 101
('/u03/oradata/MYDB/stbyredo101.log') SIZE 512M;
-- repeat log switches on PRODUCTION as necessary for standby redo
-- logs to become "unassigned"
alter system switch logfile;
-- remove one standby redo log at a time, then replace it with the
-- renamed log
ALTER DATABASE DROP STANDBY LOGFILE GROUP 10;
-- on the file system:
## clean up the old files
mv /u03/oradata/MYDB/redo10.log /u03/oradata/MYDB/old
-- rename the online redo files on the standby and add more logs to match prod
-- online redo in standbys is also overtaxed by reporting activity and log apply
alter database add logfile group 4 ('/u03/oradata/MYDB/redo04.log') size 512M;
-- issue this in the STANDBY db as often as needed to free up the online redo files
alter system switch logfile;
alter database drop logfile group 1;
-- on the file system:
alter database add logfile group 1
('/u03/oradata/MYDB/redo01.log') size 512M;
## clean up the old files
mv /u03/oradata/MYDB/redo101.log /u03/oradata/MYDB/old
-- in Production: set STANDBY_FILE_MANAGEMENT back to AUTO
alter system set STANDBY_FILE_MANAGEMENT=AUTO scope=both;
-- may want to restart the standbys here due to possible bug.
-- start log apply in standbys
ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE;
One minor tricky thing — while the add group syntax uses parentheses, the drop logfile member syntax does not:
ALTER DATABASE DROP LOGFILE MEMBER '/u03/oradata/MYDB/redo10.log'; -- does not work
with ()
DBA n00b 