MIDRANGE dot COM Mailing List Archive



Home » MIDRANGE-L » May 2014

Re: ?s regarding sparse indexes



fixed

S/O for file I/O? Yes, and also for optimization. Now that the default for the QAQQINI setting, IGNORE_DERIVED_INDEX, is *NO, S/O LFs are available to the optimizer.

This is basically the same as the sparse index - which has a WHERE clause - and we can also specify the columns to be presented by the INDEX - so this becomes almost exactly the same as an S/O logical.

We have been able to use indexes in RPG in F-specs - the newer kind of index is just as useful for I/O as S/O logicals, and also for optimization of SELECT statements that include a matching element in the WHERE clause or probably in a JOIN.

HTH
Vern

On 5/1/2014 1:51 PM, Alan Campin wrote:
If you are using SQL, use the physical and let SQL tell you what indexes to
use with the Index Advisor. Select/Omit logicals is for file I/O


On Thu, May 1, 2014 at 12:20 PM, Vicki Wilson <VWilson@xxxxxxxxxxxxx> wrote:

I'm new at a company that has launched a DDS to DDL initiative.

The idea has been introduced to replace our select/omit logicals with
sparse indexes.

The idea of a sparse index is new to me and I'm wondering about best
practices regarding sparse indexes.

The first thought that comes to mind is that I was always taught not to
use select/omit logicals. Quite frankly this has been so ingrained in me
that I'm not sure why anymore. The most obvious argument is that when
researching code it's frustrating. Some of the business logic is hidden in
the logical and being new to the environment I don't always realize what
might be happening outside of the program.

For that reason alone I'm not a fan of creating sparse indexes to replace
select/omit logicals. For review/analysis purposes - it would hide some of
the business logic.

But the idea of a sparse index also perplexes me for another reason. I
thought the idea in SQL was always to reference the table - not a logical.
And let the engine do the work. If you used sparse indexes wouldn't you
have to reference the specific index?

Thoughts on best practices and references would be appreciated. I tried a
google search and did not come up with much.

Thanks.
Vicki Wilson


--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.








Return to Archive home page | Return to MIDRANGE.COM home page

This mailing list archive is Copyright 1997-2014 by MIDRANGE dot COM and David Gibbs as a compilation work. Use of the archive is restricted to research of a business or technical nature. Any other uses are prohibited. Full details are available here. If you have questions about this, please contact