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  3. August 2014

RE: Trigger issue with authority

My gut feeling is more to do with legacy programs. If an old program
does a write to a file with an error indicator that is never checked
because we know nothing ever goes wrong except for a disk failure...

Then we put a trigger on that file that might hit an issue, or might
even reject the write after some new validation, then that old program's
got a problem.

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of
Charles Wilt
Sent: Tuesday, August 05, 2014 12:39 PM
To: Midrange Systems Technical Discussion
Subject: Re: Trigger issue with authority

Correct, job B may wait or it may throw an object in use exception
causing the update operation to fail; depending on the the appropriate
wait setting.

I disagree with your gut feeling.

I have no issues with bolting on an appropriately designed trigger
program.
Sure you need to look at any existing triggers on the same file _AND_
any existing triggers on the file the new trigger uses. But the nice
thing about triggers is that the DB tracks them for you.

Like anything else, triggers are a tool. You need to learn to use them
appropriately or they can hurt 'ya!

Charles


On Tue, Aug 5, 2014 at 11:16 AM, Briggs, Trevor (TBriggs2) <
TBriggs2@xxxxxxxxxxx> wrote:

Thanks for the clarification, Charles. So what I believe you're saying

is that if Job A issues an update that causes a long-running trigger
to fire and then Job B issues an update to the same file, then Job B's

program will wait (the default wait time for the file?) and, if it
cannot successfully update in that time, the update operation will
fail?
So, that is potentially even more dangerous than just causing a
slow-down in updates. My gut feeling is that you can never just "bolt
on" a trigger program to a file without evaluating the potential
effect on every program that touches the file.

Trevor Briggs
Analyst/Programmer
Lincare, Inc.
(727) 431-1246
TBriggs2@xxxxxxxxxxx

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of

Charles Wilt
Sent: Tuesday, August 05, 2014 11:00 AM
To: Midrange Systems Technical Discussion
Subject: Re: Trigger issue with authority

As far as a batch job making hundreds of requests within a few
microseconds...

You need to realize that when your code executes a WRITE and/or
UPDATE, control gets passed to the DB code, then to your trigger. It
returns from the trigger to the DB and then back to your code. So the

next op-code in your RPG code won't be executed until the trigger has
completed.

Thus the reason for the best practice that a trigger do as little as
possible. Having a long running task in a trigger is not a good idea.

Now, in the OP's case, besides the wait required for the CLRPFM to
complete making it a bad idea in the first place. You have to worry
about concurrency in a trigger. Since any job could cause the trigger

to fire at any time, it's likely that it will. Your tigger program
needs to follow best practices for concurrent resource use. As you
may guess, having multiple jobs randomly doing a CLRPFM on the same
table is not a good idea with respect to concurrency.

Charles


On Tue, Aug 5, 2014 at 10:11 AM, Briggs, Trevor (TBriggs2) <
TBriggs2@xxxxxxxxxxx> wrote:

Good question. I haven't used trigger programs much, so I can't say
what
happens if the file is updated again while the first invocation of
the trigger program is still running. However, it does seem like a
bottleneck waiting to happen. What happens if you have, say, a batch
job
that makes hundreds of updates to the file within a few
microseconds?

Trevor Briggs
Analyst/Programmer
Lincare, Inc.
(727) 431-1246
TBriggs2@xxxxxxxxxxx
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf
Of Hoteltravelfundotcom
Sent: Monday, August 04, 2014 6:07 PM
To: Midrange Systems Technical Discussion
Subject: Re: Trigger issue with authority

just on the point about the collision. Once i fix the authority
issue.

If one user enters a change to the Physical file, lets call it PF1,
and
the
trigger gets kicked off. The CL takes about 20 seconds to run.
recall the CL, clears the PF used to hold latest data then
re-populates via RPG prgram.

After 5 seconds another user makes a change to PF1. the trigger
kicks off again, and it wants to clear the file. Which is still
going to run 15 more seconds. Does the second trigger wait, those 15

seconds and then kicks off?

is there going to be any problem with this?

I much prefer the message queue idea but if the current way will
work, they seem to be ok with the current way.




On Mon, Aug 4, 2014 at 12:15 PM, Buck Calabro <kc2hiz@xxxxxxxxx>
wrote:

On 8/4/2014 9:12 AM, Hoteltravelfundotcom wrote:
I had a case happen that the trigger would not run.

the trigger is on a physical file which has 2 logicals to it. I
have a
PF
that will be updated when one field in the PF changes.

When change made and trigger is invoked i run a CL program which

clears my work file and then rebuilds it via RPGLE program.

that is all the CL does, CLear and run the RPG.

But got an error CPF3137 NO Authority to clear, initialize etc.

Do I need now to change the authority on that Temp file I
created?
the
current is

*PUBLIC * CHANGE

The Knowledge Centre has a page which explains what security is
required
for which operation: IBM Knowledge Center - Defining how
information
can
be accessed



http://www-01.ibm.com/support/knowledgecenter/ssw_ibm_i_72/rzarl/rzarl
ac
ctyp.htm?lang=en

There is another way to 'clear' the table; use SQL. DELETE FROM
TABLE.

--buck

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