I don't understand much about High Water Mark(HWM), please help me:
When a segment get a HWM ?. Whether we should deallocate all free spaces above HWM or just apart of them?.
The following sentence is extracted from Oracle9i Database Concept: "As requests for new free blocks that cannot be satisfied by existing freelists are received, the block to which the high water mark points becomes a used block, and the high water mark is advanced to the next block."
==> It means that we should not deallocate all free spaces above HWM, we should keep apart of it for requests for new free blocks.
I don't understand this result:
Before deallocate all free space above HWM,
dba_table.empty_blocks = 108
After deallocate all free space above HWM,
dba_table.empty_blocks = 4 ==> It's must be zero ?