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| Re: High water mark [message #20521 is a reply to message #20517] |
Fri, 31 May 2002 10:33  |
Sanjay Bajracharya
Messages: 279
Registered: October 2001
Location: Florida
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Senior Member |
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You create a table with some initial extent. As the table grows, it adds another extent defined by 'next' extent. In the long run, a table will have an 'initial' extent and multiple 'next' extents.
High Water Mark is the end of the last extent. As table grows, another extent will be added and the HWM will also be updated to the new level.
Oracle knows the HWM and during a FULL table scan, knows how much to read.
When you delete records from a table, the HWM is NOT affected. I said NOT. ONLY when you truncate the table, the HWM is set to a lower/new level. Due to this, if you are emptying the table, you better truncate the table than do 'delete * from table_name'.
Hope this helps.
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