Automatic Index Flashback (was: Re: Demand Indexes and deleting records.)

[Jay R. Ashworth]

----- Original Message -----
> From: "Nancy Palmquist via Filepro-list" <filepro-list at lists.celestial.com>

> filePro People,
> 
> I just noticed a very strange thing but it makes sense in a way.
> 
> Once a week I build a demand index with the oldest stuff in a very large
> database.  I then run through that index and delete items until I run
> out of time.
> 
> So I have an index with some items deleted and some not.
> 
> What I just noticed is that when new records are added into the slots
> where records were deleted, they seem to be included in the index. It
> makes sense in that the index has record pointers.  The data is not in
> sorted order but it is picking up the data on the record as if it should
> be in the index.
> 
> I offer this as a caution that if you are depending on a demand index to
> remain the same, you may be surprised if you are deleting records to
> find new records in their place in the index.

Well, automatic indexes do this too -- if you change the index field while
you are walking an automatic index, *it looks at the changed data* to decide
where to go next at the end of processing.  That cost me 3 or 4 days, while
coding some stuff back in 1995 or so -- that code, if it still exists, has
a comment about *exactly where in the sources for 4.2* that design flaw occurs
(the client was a 3b2 beta site, so I actually got to look it up for my bitchy
comment).

I forget now how I fixed it...

Cheers,
-- jra
-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
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