If some but not all readers re-open while an optimize is underway, this will cause > 2X temporary
space to be consumed as those new readers will then hold open the partially optimized segments at that time. It is best not to re-open readers while optimize is running my question is: 1、if the readers do not call re-open, segment file the readers will see is after merged or before merged when optimize() done 2、when old segment file on disk is removed,if old segment files are removed after optimize() done at once, How can the readers see the old data on the disk.