Re: Replication : database triggers vs log sniffing

> >voodoo wrote:
> >>
> >> Hello,
> >>
> >> Is there anyone out there who knows why database tiggers used in
> >> oracle's replication are BETTER than log sniffing used in other
> >> databases? is log sniffing faster ?? unfortunately i have no idea what
> >> database uses log sniffing . I need this information in order to
> >> convince a hopefully future user of oracle.
> >> It is Better ?!! Isn't it.
> >> any information would be very helpfull - Thanks.
> >
> >They are the same thing. The Oracle Advanced Replication Option will
> >setup triggers and packages which will generate replication logs. Those
> >logs will be used by the replication jobs to replicate the data.
> >
> >It is a normal and sensible way to implement Replication.
> >Also the performance, in my experience, is reasonably good.
>

I would say that Oracle's "Advanced" Replication was an easy way for Oracle to get into the replication market without a major rewrite. Because it was implemented out of existing user-level features such as triggers, packages and job queues, minimal server mods were necessary. Compared to a pukka server based solution (which Oracle are working on) it has the following problems (at least): 1. Sequences are not replicated
2. Once replication is up and running, it adds a extra dimension of complexity to maintaining the database.
3. Applications must be replication aware. For instance if you define a trigger which would fire at the same time as a replication trigger, the order of events is undefined. i.e. the result is undefined.

For the UNIX users out there I would say Oracle replication is analagous to a disk replication solution built out of user-level shell scripts.

James Powrie Received on Tue May 06 1997 - 00:00:00 CDT