Multiple update request - Concurrency issue

Question

Hi
One of our customer is facing a concurrency issue when multiple service instance are running. When a request comes for update, say A, tuxedo assigns the task to a free server and in meantime a similar update request comes, say B, tuxedo assigns the request to another free server. Request A caches data from DB and continue further processing meantime request B also retrieves data from DB and loads the values into cache. After sometime request A completes its job and commits the transaction and when request B tries to update the value it reports an error. This is our finding so far.
I just want to know is there any way we can make the request in sync or in other words request B see the updated value.
Regards,
Vishal

Answer 1

Hi Vishal,
Tuxedo makes heavy use of semaphores (including it's own user mode version based upon the the test-and-set instruction), and shared memory. We don't expose any APIs though that deal with those area, i.e., we just use them internally. Your servers are certainly able to use standard OS level semaphores or shared memory as Tuxedo would be completely unaware of this. If concurrent access though to a database is the major issue, I'd push that down to the database as it is in a much better place to determine what level of concurrency is safe based upon policy and not some programmers arbitrary decision about what should be serialized and what shouldn't.
You mention shared memory and I'd be curious to understand your interest in shared memory. What would you want to accomplish with shared memory?
Regards,
Todd Little
Oracle Tuxedo Chief Architect