Transaction cancellation fails intermittently on Oracle when the transaction is running a database query. This leads to stuck semaphores with the threads waiting on the database, but the database is not processing the query. Note that not every stuck semaphore is rooted in this problem, but this problem is one way that we arrive at stuck semaphores.
Steps to Reproduce
In practice, we have found that this issue is most likely to occur when reference auto-complete transactions get cancelled by subsequent auto-complete transactions.
This issue has been fixed in Eureka.
Related Problem: PRB624995