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John

I also do not know about the use of addresses. But I've dug into what data files look like to an extent.

Each record has in the first byte in storage, the flag for whether it is deleted. I think it has the value, in hex, of C0 or 80 but it has been a while. The difference there is 1 bit, on or off.

There is also sometimes an auxiliary area - none of this need matter to you, by the way. But this aux stuff has NULL capability information and info about how varying length column data is stored - it's not all in the main record for the file. So there can be a bunch of info before you even SEE any of the data.

I used to know how to worm my way down through the object addresses to see the actual data, but have forgot. And for anything you do, you really don't care - this system really takes care of you.

Regards
Vern

McKown, John wrote:
Just to be sure that I understand about the "single level store". When
an object is created, it gets an address. The MI uses this address
(which I think of as a virtual storage address) to access the object.
When that object is destroyed, the address is never reused. From my
reading, the address still points to the destroyed object. The storage
for the contents of the object is released, but the "header" now has
something that says "this object is invalid". If the object was a
permanent object, that specific address is never reused unless the
entire system is dumped and restored. If the object was a temporary
object, the address might be reused after an IPL. True? This is what I
gathered from reading Dr. Soltis' books.
Also, in a PF, when a record is deleted, the space for that record is
not used for a new record. New records are always added at the end of a
physical file. Space can only be reclaimed when the PF is re-organized.
Now for my question. Is there any way to read that deleted record? I ask
because there was an old access method on MVS called ISAM. It did not
delete records either. It simply marked the record as deleted with an
indicator in the record. But a person could use a special option which
would allow a program to read the deleted record. So I was curious if it
is possible to read a "deleted" record.
Hope everybody is having a good year, so far.
John McKown
Systems Engineer IV

IT


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(817) 255-3225 phone * (817)-961-6183 cell

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