RE: A critical Query on Triggers

Add a sequence number to your history file, and make it part of a unique key
on that file. Create a data area to hold the next sequence number. In the
trigger program, *LOCK IN(E) the data area, get the number, write it to both
the BI and AI records, increment the sequence number by 1, and OUT the data
area. Put a loop on the *LOCK IN(E) so that if the %ERROR indicator is on,
keep trying until the lock goes away. That way, no two change records will
ever have the same sequence number, and the history records will be unique,
even if two or more records have exactly the same information.


Regards,
Francis Lapeyre
Me transmitte sursum, Caledoni!




-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Vijaykrishna_Malladi
Sent: Friday, July 8, 2005 3:37 PM
To: RPG400-L@xxxxxxxxxxxx
Subject: A critical Query on Triggers


Hello folks,

I have a Query on triggers in AS400.
We have an update trigger program (coded in RPGLE) on  a Physical file which
writes 2 records for an update (Before Image, say BI and After image, say AI
of the record being updated in the PF) into another PF which we call as a
history file.
We want to process the History file in the same sequence, i.e., the BI and
AI should be in pairs. so that we can read them sequentially and by the
change code field in the 2nd file, we determine whether it is BI or AI.

My problematic situation is: Suppose if two batch programs are updating the
same file, there may be a chance that a BI for one of them is written in the
History file and before the AI is written, the BI of some other record
update would be written (even though, we have coded the write statements for
the BI & AI, immediately one after other). This may happen because AS400 is
very fast. Actually will this happen? if a trigger program is running, will
it run only in one instance? or multiple instances is also possible at the
same time?

Any help in this would be highly appreciated. Since we are executing a big
project based on this here.

Thanks in Advance,
Regards,
Vijay

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