What is an HighWater Mark

What is an High Water Mark?

Hi,
See, it's mainly used at table segment level (I say refers to). At segment level, if you think blocks are laid one after the other in series, like train or class rooms in series. The HWM is always will be in terms of Right Outer most.
I trying to provide the image.
+---- high water mark for empty table
|
P
| | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | |
--+
As you insert the data in to the table the HWM, tracks down to right side, I means increases.
+---- high water mark for empty table
|
P
| 1 | 1 | 2 | | | | | | | | | | | | | | | | |
| 1 | 1 | 2 | | | | | | | | | | | | | | | | |
--+
Now, as you see above HWM moves to right side. Once you delete the rows and commit. still the High wark mark persists there. It's limit where gives any idea up to that point the persists (blocks). When ever the Ful tablescan happens it scans up to the HWM, even when they contain no data. There will be slight difference with respect to HWM when you go for Manual Segment Space Managemet and ASSM (Keep that in mind).
For Additional thing Refer to links
Re: What is High water mark (HWM) ,use of show parameter..
- Pavan Kumar N

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