Before start this article we must know about “HWM” . After did lots of R&D i found the technical definition

Explanation in Detail: (http://www.dba-oracle.com/t_high_water_mark.html) .

The high water mark (HWM) for an Oracle table is a construct that shows the table at its greatest size.  Just as a lake has a high-water mark after a draught, an Oracle table has a high water mark that shows the greatest size of the table, the point at which it consumed the most extents.

 

Why do we need HWM ?

The high water mark (HWM) has a function that comes into play with tables that have heavy insert, update and delete activity. Every time data is changed in a table, the HWM moves to a setting in each table that shows how much free space is left in terms of blocks used and free in the segment object.

To resize any datafile to reclaim some space on the datafile. Need to check for the High water mark usage and based on that Water mark we may have to resize the respective datafile to get the space reclaimed.

We had an critical space issue on the datawarehouse environment to reclaim the space identified the datafiles using below query and resized the respective datafiles where we can get some space through this process.

Note: This is for a temporary Fix and have to plan for a better storage.

Thank you for giving your valuable time to read the above information.

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