Xiaogang Wang writes:
> Thanks to Malcolm Cohen who suggested to use a read with a blank
> I/O list. Malcolm believe that this will also skip the record (
> the data is not actually read from the disk). This sounds very
> likely to be true.
Did Malcolm say that the data is not actualy read from the disk?
I just reviewed everything he posted in this thread and I certainly
did not find words like that. It sounds very *UN*likely to be true
to me. There may be certain overhead that is avoided by having
an empty I/O list, but don't expect the physical disk read to be
avoided.
Heck, with typical disk technology, it is physically impossible
to read anything other than whole sectors from a disk. I don't
recall what typical disk sector sizes run these days (been a while
since I had to work at that level).
You will certainly have to read all of the sectors containing record
headers. If records are big enough to span multiple disk sectors,
then it *MIGHT* be plausible that you could avoid the disk read
of some of those sectors - but I wouldn't count on it even then.
Skipping a record is a logical concept. That logical concept has
connections to the underlying physical I/O, but the connection is
nowhere near as direct as you seem to be thinking.
--
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