RE: duplicate record Id's in multi user environment

Jim Franz wrote:

>> time. So the question remains, how to be absolutely sure of no duplicate,
>> yet fast to assign. Last time I did this, it was a combination key from
RPG
>> pgm data structure JOB, JOB NBR, and then timestamp (a single user could
not
>> enter 2 records within the same timestamp). (if you want file keyed in
entry

Eric N. Wilson wrote:

>Well Jim I agree that the likelihood of a user job writing twice in
>one timestamp click is impossible at this moment, perhaps they 
>will be able to in the future.

I have already been bit by this in the past.  If two machines are writing
data to a single distributed database you can indeed have the exact same
User, Job, Job number and timestamp.  Let me tell you - it's rare, but it
hurts when it happens.

Having a server job that delivers IDs is a good solution to a high volume
environment - checkpoint the number every 25 increments or 5 seconds of
elapsed time.  If the system fails, you need to write a "find the last
number used" routine to re-synchronise before first use.  For more typical
performance regimes, simply locking a data area works just fine.

If the "get the next number" routine is encapsulated in a service program,
you can change the underlying "get next" code without affecting the programs
that use the next number.  I would do this even if you decide that the code
will always be as simple as *LOCK IN, ADD, OUT.  It's easy to implement and
reinforces good design habits.

Of course, the very fastest way to do writes without worrying about
duplicates is to use a sequential file...  :-)

Buck Calabro
Aptis; Albany, NY
"We are what we repeatedly do.
 Excellence, then, is not an act, but a habit." --Aristotle


Billing Concepts Corp., a NASDAQ Listed Company, Symbol: BILL
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