Prabhat Sahu

 Profile Answers by Prabhat Sahu 

• Oct 15th, 2018

 

-- PCTFREE , PCTUSED and High Level Watermark in datablock:
------------------------------------------------------------------------------
--> HLW is a term used with table segment in DB to show the amount of datablock occupied(level) by the table data.
--> As per PCTUSED and PCTFREE mentioned for datablock, the data will fillup in datablocks.
--> when a table created(without data), the HWM level will be on left most datablock(consider the datablocks arrange horizontally).
--> After inserting few records, it fill few datablock, and HWM will increase.
--> After deleting few intermediate records, it will vacate few datablock, but still the HWM will be same. -> Till REBUILD/TRUNCATE/ SHRINK.
--> Once we will TRUNCATE the table the HWM will be on reset to initial position (left most datablock).
--> After creating a table(when its empty)
The HWM will be on left side.
|
v
+--+--+--+--+--+--+--+--+--+--+
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
+--+--+--+--+--+--+--+--+--+--+
--> After inserting few records, it fill few datablock, and HWM will increase.
|
v
+--+--+--+--+--+--+--+--+--+--+
| | | | | | | | | | |
|xx |xx|xx|xx|xx |xx|xx | | | |
|xx |xx|xx|xx|xx |xx|xx | | | |
+--+--+--+--+--+--+--+--+--+--+
--> After deleting few intermediate records, it will vacate few/part of datablock,
but still the HWM will be same. -> Till REBUILD/TRUNCATE/ SHRINK.
|
v
+--+--+--+--+--+--+--+--+--+--+
| | | | | | | | | | |
| |xx| |xx| |xx| | | | |
|xx |xx| |xx|xx|xx|xx | | | |
+--+--+--+--+--+--+--+--+--+--+
--> Once we will TRUNCATE the table the HWM will be on reset to initial position (left most datablock).
The HWM will be reset to left most side datablock.
|
v
+--+--+--+--+--+--+--+--+--+--+
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
+--+--+--+--+--+--+--+--+--+--+