In this
mode, all changes to a local log file are written synchronously to a remote log file.
This mode guarantees that switching over to the standby database will not result in
any lost data. As youmight guess, this mode may impact performance, as each log
write must also be completed to a remote log file. Oracle provides an option that will
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wait to write to a remote log only for a specified period of time, so that a network
failure will not bring database processing to a halt.
If some data loss is allowable within certain limits, Oracle Database 11g enables a
fast-start failover to occur provided that redo loss exposure does not exceed the limits
the administrator sets. As noted earlier, a physical standby database is also more
useful as of Oracle Database 11g since it is now possible to query the standby while
redo apply is active.
Unarchived redo information and the role of geo-mirroring
If you require primary site failure not to result in the loss of any committed transactions,
and do not choose to use the zero data loss option of Data Guard, the solution
is to mirror all redo log and control file activity from the primary site to the standby
site.
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