db file parallel read

官网解释：

    This happens during recovery. It can also happen during buffer prefetching, as an optimization (rather than performing multiple single-block reads). Database blocks that need to be changed as part of recovery are read in parallel from the database.

Wait Time: Wait until all of the I/Os are completed

解释：

    db file parallel read 这在恢复期间发生。 它也可能在缓冲区预取期间发生，作为优化（而不是执行多个单块读取）。 从数据库并行读取需要作为恢复一部分进行更改的数据库块。