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high water mark [message #611597] Fri, 04 April 2014 05:23 Go to next message
pavanintouch
Messages: 5
Registered: March 2014
Location: hyderabad
Junior Member

Hi,
Can some one explain me what is high water mark?
Re: high water mark [message #611598 is a reply to message #611597] Fri, 04 April 2014 05:43 Go to previous messageGo to next message
rc3d
Messages: 191
Registered: September 2013
Location: Baden-W├╝rttemberg
Senior Member
What is High Water Mark in Oracle?

Answer:

1. High water mark is the maximum amount of database blocks used so far by a segment. This mark cannot be reset by delete operations.

2. Delete Table operation won't reset HWM.

3. TRUNCATE will reset HWM.

4. The high water mark level is just a line separate the used blocks and free blocks.

The blocks above the HWM level is free blocks, they are ready to use.
The blocks below the HWM level is used blocks, they are already used.

I hope now you understand well. see the below example.

for example, if you delete some huge records from the database, that data will delete but the blocks are not ready to used, because that blocks are still below HWM level, so delete command never reset the HWM level,

At the same time you truncate the date, then the data will delete and that used blocks will goto above the HWM level, now its ready to used. now they consider has free blocks.

more
http://asktom.oracle.com/pls/asktomf?p=100:11:0::::P11_QUESTION_ID:492636200346818072
Re: high water mark [message #611602 is a reply to message #611598] Fri, 04 April 2014 06:08 Go to previous messageGo to next message
pavanintouch
Messages: 5
Registered: March 2014
Location: hyderabad
Junior Member

thank you very much.
now i got clear idea.
Re: high water mark [message #611622 is a reply to message #611602] Fri, 04 April 2014 10:12 Go to previous messageGo to next message
Michel Cadot
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Registered: March 2007
Location: Nanterre, France, http://...
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Account Moderator

This is segment HWM, you also have file HWM, checkpoint HWM and so on...

Re: high water mark [message #612428 is a reply to message #611622] Fri, 18 April 2014 06:13 Go to previous message
pavanintouch
Messages: 5
Registered: March 2014
Location: hyderabad
Junior Member

can u explain/share about it
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