Re: Add fields to physical file without exclusive lock _ formerly Re: Stupid question of the century

And Oeps we are back in the S36 and the C++ Structs ERA we where all so happy that we got out since the late 80's.

Eduard.

________________________________
From: Alan Shore <AlanShore@xxxxxxxx>
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Sent: Monday, May 11, 2009 9:17:19 AM
Subject: Re: Add fields to physical file without exclusive lock _ formerly Re: Stupid question of the century

Thanks for your reply Denis
The process you described DEFINITELY makes sense, and to a certain extent
we are already doing this.
Whenever we need to add fields to an existing file, we also add extra
fields (alpha) to the end, of varying lengths
The unfortunate thing is, we never seem to  add enough
However I like the idea of adding ONE LARGE field, and then taking bits and
pieces of it as is needed
I found it interesting that you no longer recommend this method any more.
Can you say why


Alan Shore
Programmer/Analyst, Distribution
E:AShore@xxxxxxxxxxx
P:(631) 200-5019
C:(631) 880-8640
"If you're going through Hell, keep going" - Winston Churchill

midrange-l-bounces@xxxxxxxxxxxx wrote on 05/11/2009 08:30:55 AM:

Hello,

I have done that (or at least something quite close). I had a similar
challenge in the early 90's when we implemented level checking. I had to
devise a way to add filed to a file without creating a level check while
leaving level checking on.

Here is what you could do.
- For the first time, you will still need exclusive access to the file
- you had one big alpha field to the file (1000 char. or more)
- you recompile the file and all programs that use it

Now you are set so you can had fields o the fly.

- You define an external data structure (basically a PF with no data in
it) that redefine the big alpha filed added earlier
- You use that external DS in the D spec of the program to overlay the
big field
-- This way, there is no level checking being done on the external data
structure since it is not on the F spec
- When you need a new field, you just modify the external data
structure, recompile it (it is never locked)
-- be sure to add new fields at the end and to never move a field.
- then you create a one shot program to initialize the new field
(putting all "0" in it or whatever)
- you must only recompile the programs that access that new fileds.

Of course, there are some limitation to this technique. The biggest is
that no filed added can be part of a key.

I do not recommend this method anymore, but it does achieve what you
want:
- Can add filed to a file while it is locked
- The only programs that need to be freed and recompile are those using
the new fields
- imply very little change to all existing program

I hope this make sense to you.

Denis Robitaille
Directeur services technique TI
819 363 6130

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Alan Shore <AlanShore@xxxxxxxx> 2009-05-09 13:18 >>>

Hi guys
I've just been asked the following question by my boss's boss
Is there anyway to add new fields (columns) "on the fly" to an
existing
file, without having an exclusive lock on that file.
In other words, the file is still being used while the field is added
I know that chgpf is out of the question (unless someone proves me
wrong).
I know that SQL is also out of the question (ALTER TABLE x ADD
EXTRAFIELD
DEC(7, 2) NOT NULL DEFAULT 0) - again unless someone proves me wrong
If anyone knows of any way, any language, any procedure, any function
to
achieve this, please drop me a line.

Thanks in advance


Alan Shore
Programmer/Analyst, Distribution
E:AShore@xxxxxxxxxxx
P:(631) 200-5019
C:(631) 880-8640
"If you're going through Hell, keep going" - Winston Churchill
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