The high water mark is the last extent that has been allocated for a
database object such as a table. For example if I create a table and add
1,000,000 rows to it and then delete 999,000 rows from the table the high
water mark is the last extent that the table took up when I had 1,000,000
rows in it. The upshot is that if you have a query that does a full table
scan it will scan up to the high water mark and so a 1,000 row scan in our
example becomes quite expensive because it is scanning the area that Oracle
had allocated for the 1,000,000 rows. No there is no low water mark because
the mark is covered over by the high water mark :-).
Jim
"Kasp" <kasp_at_epatra.com> wrote in message
news:a4fl3e$jj2$1_at_newsreader.mailgate.org...
> Hi,
> Can someone give me what does "high water mark" mean?
> What is it used for ?? Is there something called "low water mark" also?
>
> thanks.
>
>
Received on Thu Feb 14 2002 - 00:54:57 CST
