I have
used both.
Replication, like archive log movement , happens whenever you set it up
to happen. That can be anywhere from every minute to once a day to
beyond. It just depends on your needs. In the case of my old job, we
had replication happening at different times for different
tables. Our key table was replicating IMMEDIATELY upon any
changes to the parent table. This happened via
trigger. Other , not so important tables, would replicate at
anywhere from 30 to 60
minutes. We did this using scheduled jobs.
I see
two real nice advantages of replicated databases. One, they are
accessible. i.e. you can run reports, queries, etc on them.
They are nothing more than instances that get updated via a foreign
database. Two, depending on what kind of software you use, you can
update the database from an outside source. We used to have data
sent down from our DB2 database into our Oracle database using an oracle product
called Replication Services (nothing more than triggers and a specific data
structure) and an IBM product called Data Propogator.
Archive log transport for standbys can happen in
multiple ways also. The newer oracle versions support direct archiving
from a production database to a standby database. I have not tried this
yet but we are looking into it. Our current standby databases are
brought up to date with a shell script that is scheduled via cron every 20
minutes.
The thing about the standbys, they are all or
nothing ... you can not just say I want only tables 1-10 to be updated.
They all are. Also, in the older oracle versions, the standbys could not
be accessed via software so you could not use them as any sort of read only
database. This is not the case in a replicated database. But,
they are also very easy to rebuild and resetup. Just copy your production
files over, create a standby control file, and bring the databse up in standby
mode. Very easy.
Now... which would I recommend ??? Depends
on your needs.
If you really need to access that copy of the database
for other purposes and you only want certain tables to be updated, then I would
consider replication. If, on the other hand, you do not have to
access the data (until such a time as your production gets killed and you need
your standby up) and you need a fast way to rebuild the second database, I would
suggest the Standby approach.
Kevin
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