Re: Interesting Benchmarks -- SQL, RPG, Journaling, and Triggers

Walden H. Leverich wrote:

Listening to a concurrently podcast this morning I had an interesting
thought, how do you handle the case where the row didn't exist when you
chained for it, but is written by another process before you insert it?

You get an error on the write. It's an application design issue - usually the chain then write isn't done to try to avoid collisions, but rather to attempt to aggregate multiple records, usually on history files. While it's possible that two processes could choose to use that exact millisecond to attempt to write the same record, in practice it's either vanishingly rare (user maintenance programs) or non-existent (batch updates).

That's not to say that such things can't happen. If your design is such that collisions are possible, then you test the %write for a error. If you want to avoid the chance of an error, then you use a semaphore. Lock a data area before you begin the chain/update./write process. But the overhead there is high - I'd stick with checking the write.

Joe