Inline

At 05:24 PM 3/31/2004 -0500, you wrote:
On Tue, 2004-03-30 at 18:08, Vern Hamberg wrote:
> AFAIK, physical files are not the same as flat files. They ARE the same as
> tables created through the SQL CREATE TABLE statement.
>

Not entirely true. For example, there are two code paths used for
selecting from a table scan.

My comment was really in the context of differentiating from flat files. The difference I meant to highlight is that PFs have a record structure (fields defined as part of the PF), flat files, a la S36, do not - need to be defined in a program. If that's what was meant by flat file.


Your point is well-taken, however, as my statement was too general. SQL tables are physical files with some attributes added/different - DSPFD shows the differences - still a physical file, but has an SQL attribute that a flat file (created using RCDLEN, not DDS source) will not, but it is externally described, just as a PF defined with DDS.

If you are selecting on a numeric value, and that table was built with
DDS, then the optimizer is forced to use the 'Derived field' selection.
If the table was built with SQL, then the table scan can use the Direct
selection. The code path is shorter on the Direct selection.

So this is one of the advantages Rick probably wants to know about, eh? Cool.


> And keyed logical files and SQL indexes are essentially the same thing -
> B-trees.

The Access Path part is, but most keyed logical files show up as views,
even when no mapping takes place. And sometimes, they don't even show up
as views. But the optimizer still considers non-sparse access paths
during the optimization phase.

Show up in OpsNav? I suppose - Hmm, that's interesting, looking at the "description" item when I right-click. Although there is an access path tab, it does not show the actual key fields - but it does show the key length - certainly this could be displayed better? And the definition tab can't generate a statement - of course, as it explains. Worth looking at once, IMO.


The priority in the optimizer for looking at available access paths - is it still based on age? I think that's what it was. (and probably other factors)



As an Amazon Associate we earn from qualifying purchases.

This thread ...

Replies:

Follow On AppleNews
Return to Archive home page | Return to MIDRANGE.COM home page

This mailing list archive is Copyright 1997-2022 by midrange.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 on our policy page. If you have questions about this, please contact [javascript protected email address].

Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.