Syntax is simple:
oracle [prod] backups $ sqlplus / as sysdba
SQL*Plus: Release 126.96.36.199.0 Production on Fri Sep 16 07:14:23 2016
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Oracle Database 11g Enterprise Edition Release 188.8.131.52.0 – 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> alter system set archive_lag_target=900 scope=both;
When do you set this and why? Here’s my take:
This parameter forces a log switch every X seconds – 900 seconds in the example above.
If you have a variable load, not at all unusual in fact from my experience most databases have a great variation of redo log ver time, at times generate. During the hours of operation when redo log generation is at it’s peak it is generally advantageous to increase the size of your redo logs and increase the number of groups.
Then when the database idles down, if you do not set ARCHIVE_LAG_TARGET the database may not experience enough activity go force a log switch. ARCHIVE_LAG_TARGET takes care of this for you.