RE: Logical file index size too small? -- MIDRANGE-L

Some of the logicals could be sharing access paths with logicals with the   
leftmost key the same as the logicals in question.  So if you have a   
fileA with key1, key2 and key3, and the file in question is keyed by key1   
and key2, there is a good change that the one with the lesser amount is   
sharing an access path.

Bradley V. Stone
bvstone@taylorcorp.com

 ----------
From:  Buck Calabro
Sent:  Wednesday, December 10, 1997 1:51 PM
To:  bvstone
Subject:  Logical file index size too small?


Hello again!

We've got a physical file with 2.7 million records and 10+
logical files built over it.  In an attempt to speed up
processing, we're analysing which logicals we can eliminate.
While doing a DSPFD, I noticed that the index size for some
of these logicals is really small: 16384.  This doesn't
make any sense because the key length is 36 bytes: I'm
expecting something closer to 95 megs!

Here's the section of DSPFD under Access Path statistics for
logical file TRBRSQ08:

Index size  . . . . . . . . . . . . . . :             16384
Access path valid . . . . . . . . . . . :            Yes   
                     

Implicit access path sharing  . . . . . :            Yes   
                     

  Access path journaled . . . . . . . . :            No   
                      

File owning access path . . . . . . . . :     COMTST200/TRBRSQ08
Member  . . . . . . . . . . . . . . . . :            TRBRSQ08   
                

Shared access path attributes   
                                                

  Maintenance . . . . . . . . . . . . . :            *IMMED   
                  

  Access path recovery  . . . . . . . . :            *NO   
                     

  Force keyed access path . . . . . . . :            *NO   
                     

  Keys must be unique . . . . . . . . . :            No   
                      

...
Based on file . . . . . . . . . . . . . . :            TRBPHY01
  Library . . . . . . . . . . . . . . . . :            COMTST200
  Member  . . . . . . . . . . . . . . . . :            TRBPHY01
  Logical file format . . . . . . . . . . :            ZTRBRS08
  Number of index entries . . . . . . . . :               2664901

How can this be right?  The index has 2.7 million records and
is only 16k in size?  Another logical, TRBRSQ01 has a key length
of 4, and it looks like:

Index size  . . . . . . . . . . . . . . :                    7933952
Access path valid . . . . . . . . . . . :            Yes
Implicit access path sharing  . . . . . :            No
...
Based on file . . . . . . . . . . . . . . :            TRBPHY01
  Library . . . . . . . . . . . . . . . . :            COMTST200
  Member  . . . . . . . . . . . . . . . . :            TRBPHY01
  Logical file format . . . . . . . . . . :            ZTRBRS01
  Number of index entries . . . . . . . . :               2664901
  Number of member accesses . . . . . . . :                     0

This looks much better: 2.7 million * 4 bytes = 10meg.  I've got
7.9 megs... close to what I expect.

I can see that RSQ08 is sharing it's access path, but it's being
shared with itself!

So, my question is: what can make an access path size so much
smaller than it should be?

Buck Calabro
Commsoft

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