RE: (RE): Calculating LIOs
- From: ryan.gaffuri@xxxxxxxxxxx
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 13 Aug 2004 17:18:29 +0000
How do you tell what the HWM is of indexes? I did not see a blocks column in
DBA_INDEXES?
Also, I would assume that an 'index full scan' also reads up to the HWM. I have
not been able to figure out what the difference between an 'index fast full
scan' and an 'index full scan'. I thought it was that a fast full scan read at
your multiblock read count and a full scan read 1 block at a time. However,
some people on here said that a full scan can read at your multiblock
read(however, I have never been able to get this to happen with several tests)?
-------------- Original message --------------
> Ryan,
>
> D'oh, I should have mentioned the HWM (High Water Mark).
>
> In the case of a FULL TABLE SCAN (or a FAST FULL INDEX SCAN on an =
> index), Oracle will read up to the HWM. That is, the point at which =
> data is now or has ever been stored. Blocks above the HWM are known to =
> be empty, so Oracle does not read them. If you have a table that =
> contained 100 million rows, and you delete 80 million of them, the HWM =
> will still be at the point where it was when the table contained 100 =
> million rows. One can lower the HWM by re-organizing the table. In the =
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