RE: access path

["jt" <jt@xxxxxx>]

(Relying on memory has it's disadvantages.. memory of the human kind,
anyway...;-)  I thin' this is similar, if not same, as what I saw (on S/38?)
when I did DMPOBJ way back when.  Other DB will have similar, but level of
detail in iDB2 is really outstanding.  The statistics they collect on
file/key usage SURE has IMPROVED over the years and is, no doubt, used to
aid query optimization.

I think the term "access path" is not really so hidden, and probably derives
from the concept of ODP (Open Data Path), being is the term for how HLL
programs access the data through an index (even in the case of arrival
sequence, too).  I conceptualize the access path as the *QDDSI with
associated info.  Thing I find interesting is *QDDS!  Have NO ideer why
there'd be ANY kind-a data space involved with a LF/access path...!?!

Never "played" with SST much and don't much have time lately, or I might be
tempted to knock knees...;-)

Btw, anybody recall if implicit AP sharing comes into play when 2 LF share
major keys.  Meaning:  If you have a LF by customer, and another by
customer/order (with same SLTOMT), don't these implicately share the same
AP...??  My recollection is that they do, (but wouldn't bet even a
donut...;-).

Cheers,


| -----Original Message-----
| [mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of Vern Hamberg
| Sent: Thursday, April 24, 2003 9:29 PM


| Try DMPOBJ on a traditional logical file - you'll see 5 component
| objects,
| some internal, some external. There's
| *FILE (MI type 1901) - a kind of header, I think - this is the external
| object type - DSPFD gets stuff from here
| *FMT (MI type 1951) - describes the field layout - DSPFFD works from this?
| *MEM (MI type 0D50) - cursor (member?, sort of, or pointers to?) RTVMBRD?
| *QDDS (MI type 0B90) - data space
| *QDDSI (MI type 0C90) - data space index
|


| DMPOBJ does not show the actual data - you can get to it in SST but I'd
| need to dig a little to remember where everything is. But you can
| take the
| names of each section into SST Dump/Alter/... and see some interesting
| things. Do we hear knees knocking?  <g>