Detached datasets and DRDA compliance -- MIDRANGE-L

This is an interesting point, Steve.

> From: Steve Richter
> 
> I dont think it is an openness issue.  DRDA, I am guessing, is part of
> a server centric architecture.  Since the release of  ADO.NET ( 5
> years ago ) and probably SQL Server 2000  Microsoft has gone with the
> detachable dataset approach to database serving.  They say such a
> database setup is more scalable and is more compatible with server
> farms.

Not sure yet about the server farms issue... I need to think about that.
But from a standpoint of pure server load, you're saying that the
overhead of storing the result set on the server and sending it over to
the caller on a request by request basis is higher than that of creating
the entire dataset and shipping it as a detached set.

On face value, you seem to be correct on that.  Of course, that's really
only useful when you have bounded sets; that is, sets of data where the
requester already knows the beginning and end.  That's a bit different
than the concept of a scrollable cursor, or even an updateable cursor.
Detached commitment control isn't going to work very well.

But for that segment of the application suite that is read only on small
but complex datasets, I can understand the detached set concept.
However, since you still need both scrollable and updatable cursors for
any sort of real development, this argument against server-side cursors
(and DRDA) seems to be less feasible.


>  For example, the server side SQL Cursor is still supported by MS, but
> its use is discouraged and is not a part of the .NET framework.  You
> have to roll your own.  The theory being that the server farm can
> serve out a subset of the database as a dataset to the client very
> efficiently.  The client then orders and joins the datasets as it
> wishes, using the client's resources.  The server side cursor, with
> all its built in functionality, puts a heavy load on the server.  So
> it does not scale well.

This is even more interesting.  You're saying that the client is more
equipped to join and order the data.  I'm not sure of all the database
architecture involved here; but it seems like you're dividing the
workload of the SQL engine from selecting data on the one hand and
sorting it on the other.

And that doesn't make sense at first glance, especially on a join,
because your selected data on joined tables would be limited by the
results of the initial select.  Of course, I've never believed in the
concept of distributed databases anyway, except in extreme
circumstances.  Just think of it... if the three tables of a join are on
three different machines, then the result of the first join must be sent
to the second machine, which in turn must send both datasets to the
third machine, which then sends all three datasets to the client, which
only THEN begins ordering them.

Obviously, modifiers like HAVING and "FIRST N ROWS" wouldn't be able to
reduce traffic and processing if the ordering were all client side.

To me it seems like what is happening here is that as you add servers to
a database, the processing requirements exponentiate and to offset that,
Microsoft will need to use the client CPU cycles as part of the database
access mechanism,.  That's about as non-scalable as I can imagine, and a
neat way to lock clients into the servers.  Wow... you can't be a client
on our server unless you also do a bunch of the work!

Hee hee!  That's like saying you can eat at our restaurant, but you have
to wash the dishes, too.

Joe