Question - What Is A Parallel Index Build?
Answer -
The data for the index is read in parallel by several server tasks to perform the index build as quickly as possible. Only one parallel index build can be carried out at a time - if several CREATE INDEX statements are executed at the same time, these other indexes are then processed by only one server task. This is noticeably slower than a parallel index build. Therefore, you should always ensure that indexes are only created successively.