Checking for cancellation during execution

You can call the isCanceled() method to check for user cancellation. Typically you check for cancellation from the method that does the main processing in your UDx before beginning expensive operations. If isCanceled() returns true, the query has been canceled and your method should exit immediately to prevent it from wasting CPU time. If your UDx is not running fenced mode, Vertica cannot halt your function and has to wait for it to finish. If it is running in fenced mode, Vertica eventually kills the side process running it.

See C++ example: cancelable UDSource for an example that uses isCanceled().