"Serge Rielau" <srielau_at_ca.eye-be-em.com> wrote in message
news:cbei9g$6b7$1_at_hanover.torolab.ibm.com...
> You cannot compare federated with RAC or SMP.
> Federated databses are not federated because it's nice or because it's
> preferred technology.
> They are federated is by necessity.
> If you take a look at health care, a lot of the data cannot be
> replicated to a central store for leagal reason. It may or may not be OK
> to query the data directly (store it in the DBMS's cache) but copying
> the the data to be stored persistently is a no-no.
> So federation is all about coping with an imperfect world (from the
> DBMS' point of view).
>
> DB2 II can indeed push parts of the (optimized) query to the remote
> side. It works not all that different from the shared nothing algorithms.
> The difference is that instead of shipping "DB2 byte code" to the
> database partition to be executed. DB2 II reverse engineers the remote
> DBMS' SQL dialect and uses the remotes native client interfaces to pose
> the query.
> Doing a join between a Oracle and SQL Server can mean:
> a) Pull the data to DB2 II , then join locally
> b) Pull the data from SQL Server to DB2 II, push it to Oracle and join
> on Oracle
> c) Reverse from b)
>
> To do this the DBMS has to know a fair bit about the remote DBMS
> capabilities.
> E.g. if DB2 II based it's decision on a hash-join costing but the remote
> doesn't know what that is things go sour.
>
> In a life sciences space there often isn't even any choice. The remote
> side (which may not be relational to start with) may have certain
> functions (like detetcing a gene-sequence match) which DB2 II does not
> have and which can-not or must not (IP) implemented in DB2.
> In this case a fucntion mapping is provided to model teh foreing
> function and DB2 II knows that any plan must involve pushing the foreign
> function to it's native source.
>
> The remise in this case is that the user does not need to worry about
> learning the remote's interfaces or mix query languages.
>
> Cheers
> Serge
> --
> Serge Rielau
> DB2 SQL Compiler Development
> IBM Toronto Lab
Did I miss something? What is DB2 II?
Received on Thu Jun 24 2004 - 08:03:46 CDT
