Question - Why May It Take A Long Time Until A Task Is Available Again After You Cancel The User Task To Cancel The Creation Of An Index?
Answer -
If you cancel a CREATE INDEX statement, the cancel indicator is set for the user task. However, before the task can be re-released, it must clear all index lists that were created before by the server tasks for the index build.
This ensures that all of the structures that are no longer required are deleted from the system after you cancel a CREATE INDEX statement. This may take some time depending on the number and size of the index lists.