• Subject: Re[2]: Logical file index size too small?
  • From: Buck Calabro <mcalabro@xxxxxxxxxxxx>
  • Date: Wed, 10 Dec 1997 19:36:00 -0500

>> 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!
>> 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?

>You have found one of the wonders of OS/400 (Perhaps one of the best
>things at that).  The *LF that you are examining is sharing an access
>path with another file.  Most people use the word Access path and
>Logical file interchangibly, which is really incorrect.  You can have
>multiple logical files sharing an access path as long as the least
>restrictive *LF is built first.  

Yes, I can see that it is a shared access path; the problem is that
file TRBRSQ08 is sharing the access path of file TRBRSQ08.  That
is a bit confusing.


>    In my opinion, you are better off spending more time figuring out
>how to share those access paths, than to delete a LF that you really
>need but you are deleting it for speed.  You get the speed and
>accessibility by sharing of access paths. 

Actually, I agree.  We've been doing so many mods that we have lost
track of which logicals are no longer used; we're not looking to re-write
programs just to avoid one or two logicals.  This is more of a curiosity
issue than an applications issue.  It looks as if V4R1 has made some
speed improvements in the database engine, and this "small" index
size is an artifact of those changes.  

Buck Calabro

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