Re: Questions for Oracle advanced replication

Hello Tapan ,

Thanks for your reply. Now I try to mention my question more clearly.

I plan to create a failover infrastructure by using 2 fully replicated Database DB1 and DB2. Now DB1 has lost the connection to DB2 and one client session tries to update DB1 in a transaction A. Oracle system treats the transaction as deferred, put it into a queue. Since no network connection to DB2, transaction A can not apply on it.

Suppose we use serial propagation, Oracle will work in two-step commit method. Is that right ? So transaction A should not be seen on DB1,that means the query for the same data should display the value before the transaction A starts. This will keep the DB1 and DB2 identical. However any update attempt will be deferred by putting the replication job into a background queue, and resources held by the transaction will still be occupied. Say in a OLTP env. perhaps all the system resources will be run out if the situation lasts 3-4 hours or a day. And than I get my conclusion: We can not use 2 fully replicated Oracle Server to form a Failover infrastructure whatever configuring them, since if any one of the two is not available, the whole effect is the database becomes read-only.

Hope I am totally wrong. Otherwise I just get a task from my manager that can not be implemented.

regards,

Sam Shi

Tapan Trivedi wrote:

> Shi,
> Hi. I have answered your questions in the body of your message to the
> best of my abilities.
>
> Shi yousong wrote:
> >
> > Hi,
> >
> > I am involved in a project to setup a replication infrastructure and
> > plan to use the Row-Level async replication facility to implement a
> > failover Oracle database infrastructure, so any change to the DB1 will
> > be propagated to DB2 and vice versa. Here the questions are raised.
> > What will happen if the connection between DB1 and DB2 is cut off?
> > a. Say transaction A updates a table in DB1. Now can the transaction
> > A be seen on DB1 when DB2 is not available? How about the resources
> > occupied by transaction A ? released or still held on ?
>
> You mentioned that you are planning to set up 'async' replication.
> This means that even if DB2 is not available the replication jobs will
> be queued up and when your destination (DB2) is accessible it will push
> them according to the parameters specified by you.
>
> > b. At the moment if DB1 and DB2 are identical to each other ?
> GOOD!!??!!
>
> > c. After 2-3 hours, the connection is restored for example, can Oracle
> > automatically make the 2 DB consistent again?
> > From what I have experienced it does. You might have the db which is out of sync and then you will have to sync it (which is a bit of a pain) but you generally do not lose any data if thats what you are afraid of.
>
> Hope this helps.
>
> Tapan H Trivedi
> > Thanks in advance.
> >
> > Database Developer
> > Sam Shi
Received on Tue Sep 28 1999 - 23:38:04 CDT