On Aug 8, 2012, at 18:51, Shmuel Metz (Seymour J.) wrote:
>
>> Does this mean that if the current record spans several blocks,
>> setting the z byte causes enough intervening blocks containing
>> enough segments to be skipped that the block read contains the first
>> segment of the next record?
>
> No; TTR1 will access the next physical record. BSAM doesn't deal with
> the RDW.
>
In:
http://publibz.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/DGT2D4A0/3.8.7.8
(which I trimmed too much and, now that I read the outline
hierarchy, refers to PDSEs), I read:
3.8.7 Processing a Member of a PDSE
3.8.7.8 Using the POINT Macro to Position to a Block
The POINT macro positions to the first segment of a spanned
record even if the NOTE was done on another segment. If the
current record spans blocks, setting the z byte of the TTRz
field to one lets you access the next record (not the next
segment).
So I conclude that if the current "block" (itself a slippery
concept with PDSEs) contains only an interior segment of a
spanned record, POINT to a TTRz will cause the following READ
to read the block containing the first segment of that [logical]
record, and POINT to a TTR1 will cause the following READ
to read the block containing the first segment of the next
[logical] record. It's still pretty amazing.
THis could be a point of incompatibility between PDSE and PDS.
Who keeps spanned records in a PDSE or PDS, anyway?
-- gil
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