Re: clustering and high availability?

Mike wrote:

> We're starting a project at work moving VSAM to RDBMS. The choice
> is between DB2 and Oracle. It seems like the Oracle RAC is a better
> cluster choice with it's share everything rather than the DB2
> share nothing. Please post some opinions on this and/or other
> points of difference/intereste between the two DBMS.
>
> Mike

Before you make this decision you need to test your application in a RAC environment and see how the memory interconnect works.

Assuming it is a well written scalable application consider the following:

Shared Everything:
The more nodes I add the mean time between failures goes up

Shared Nothing:
The more nodes I add the mean time between failures goes down

Shared nothing makes the problem worse ... not better

Shared Everything:
Change the number of nodes and no change need be made to the database.

Shared Nothing:
Change the number of nodes and bring the server down while you re-federate the data.

DB2 is not in the ballpark unless running on OS/390 where it is, in fact, shared everything. If shared nothing was better you'd think IBM would have used it on OS/390 too: They didn't. But who can afford to cluster mainframes?

-- 
Daniel Morgan
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