"MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx> wrote on 05/13/2016
09:15:42 AM:
... you can have thousands of views without any performance decrease.
I've heard statements like this before but such statements can
give the wrong impression. When we hired IBM to help us with our
performance issues and when we contracted for SQL training we kept being
told this and we took it at face value. Now that the performance analysis
has been completed, we are finding out a different story -- or, at least,
a clearer picture of the facts.
I agree that simply having a view (i.e., the fact that it exists)
does not add any overhead to the system beyond what having any other new
object added to the system would create. Meaning, I know that a view
object does not have to be maintained by SQL as rows are added, changed,
and deleted in the table or tables on which the view is based. From that
standpoint, there is no performance decrease and if that is all that is
meant when such statements are made then no falsehood is being given.
However, such "blanket" statements (i.e., without caveat as to the type of
performance overhead being referenced) are very much misleading. In fact,
we were also told many times -- and in no uncertain terms -- that opening
a view has negligible performance impact as compared to opening a
DDS-based logical file. Again, now that the performance analysis has been
completed, we take exception to that statement, too.
Now, we may still be lacking in our understanding of what is going
on under the covers of SQL, however we are now shying away from creating
views willy-nilly as the spirit moves us. The reason is because we now
understand that a view has to be rendered at the time it is opened and
such rendering can have (and has had, in our case) a major performance
impact on the system.
Sincerely,
Dave Clark
int.ext: 91078
direct: (937) 531-6378
home: (937) 751-3300
Winsupply Group Services
3110 Kettering Boulevard
Dayton, Ohio 45439 USA
(937) 294-5331
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