Re: Implicit Access Path Sharing

[Larry Bolhuis <lbolhui@xxxxxxx>]

Mark,

   When LFs are created with CRTLF (as opposed to via SQL) access
paths are shared when the key fields of the file being created match
those in an existing access path. For example an LF being created for
key fields 'A' and 'B' would share an existing access path for LF with
keys 'A' 'B'(obvious case) but it would also share with LF that has
keys 'A' 'B' 'C'.  It would NOT share an access path with LF keyed 'D'
'A' 'B'.  Additionally other attributes must match.  These include
sequence (ascending/descending), Select/Omit and Dynamic Select.  In
some cases certain attributes may be overriden.  I have seen Dynamic
Select ignored when the existing access path does not use it.

   I don't believe the format name has any effect. For example it you
have a PF with fields 'A' through 'F'.  LF 1 has keys 'A' and 'B' and
includes fields 'A' 'B' 'C' and 'D'.  LF 2 with keys 'A' and 'B' but
selecting fields 'A' 'B' 'E' and 'F' would still share the access
path.  Remember that the access paths select and sequence ROWS. 
Column selection is independant of the access path.  We RPG types tend
to equate access paths with LF and this is not the case.

 - Larry

Mark Lazarus wrote:
> 
>  Can anyone explain when Implicit Access Path Sharing is not used?  Would
> it be used when creating the identical *LF, but the fields are specified in
> the DDS?  How about if the format name is different?  According to my
> observations the latter would not share the AP.  Why not?
> 
-- 
Larry Bolhuis         | What do you want to reload today?
Arbor Solutions, Inc  | 
(616) 451-2500        | Two rules to success in life:
lbolhui@ibm.net       | 1. Never tell people everything you know.
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