Re: SQL Views worth it?

Hi,

These nesting, or cascading views are exactly my circumstance, and the apparent slow response time
are due to using them (I believe), and prompted my original post.
As advised, I have reviewed the Index Advisor and created indexes that appear there but haven't seen any appreciable
improvement.
As for the backup and restore issues that have arisen in this discussion, I haven't gotten that far in system testing.
I'm anticipating issues though because the physical files underlying these views are in different libraries,
and there is nothing I can do about that.

I appreciate the advice and broad discussion that has resulted from my original post.

Best Regards,

Thomas Garvey

On 8/27/2018 2:42 PM, Nathan Andelin wrote:

Evan,

I'm not aware of any IBM reference that documents this condition. Maybe
"failure" is too harsh of a term. Restore procedures will complete ... but
only after time consuming recovery from Job Log errors that identify the
SQL views that could not be restored. In our case that may be dozens of
views.

I am surprised that this issue is not more well known. I think that you
could test this yourself by creating nested views, then trying to save and
restore them. Maybe it's only manifested after nesting to a certain level
or more. It was just one of those things that we noticed as we were
designing and deploying new databases.

I define nesting (or cascading) as meaning the output of one view being
used as input for another. A chain of queries. For example, the result set
generated by view A may be queried by view B, which may be queried by view
C, which may be queried by view D, which may be queried by view E.

I believe this is one way for developers to have more control over what
occurs in the query processor. You can use your knowledge about the
database and its indexes to improve the optimization of the query processor.

Nathan.



On Mon, Aug 27, 2018 at 11:53 AM, Evan Harris <auctionitis@xxxxxxxxx> wrote:

HI Nathan

you say that Nested views as not able to be restored; do you have an IBM
reference to support that or explain why that might be ?

Do you have a simple example of how I might re-create the restore issue so
I test the scenario ?

I'd really like to understand this restore issue so being able to re-create
the problem would be a great start.


On Tue, Aug 28, 2018 at 5:00 AM Nathan Andelin <nandelin@xxxxxxxxx> wrote:

On Sun, Aug 26, 2018 at 3:33 PM, Evan Harris <auctionitis@xxxxxxxxx>
wrote:

Hi Nathan
What release did you encounter this issue in and was there a problem

report

to IBM ? What was IBM's response if it was reported ?

I guess if this is really the case then I would like to understand the
issue more deeply in order to take preventative measures.

Hi Evan,

We're on 7.3 and our PTFs are pretty-much up to date.

The issue is that Restore commands are not able to resolve SQL view
dependencies when they are nested, even if they are defined within the

same

library. Nested (or cascading) views are very elegant and really slick

from

a design and functional perspective. They're a lot more readable and
understandable than creating a single SQL view from long and protracted
query logic that you might code into a program or put into a single view.

We finally settled on our maintaining a script to rebuild nested views
after physical files have been restored.
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