Re: SQL Existence Check

[Vernon Hamberg <vhamberg@xxxxxxxxx>]

CHAIN is basically SETLL and READ, so the difference is the time to read
the record. Mileage will vary, based on record length and datatypes. What
were your fields in the file in question?

The other factor here is that SETLL will have less IO than CHAIN - possibly
only to the index (sorry, logical file). This can affect others' access to
DASD.

At 08:56 AM 3/12/02 -0700, you wrote:
> > From: <David.X.Kahn@gsk.com>
> > Nathan wrote:
> >
> > >> Why not use a CHAIN?
> > >
> > > You took the first thought that came to my mind and put it into
> > > words <smile>.  Or, why not use SETLL for better performance?
> >
> > Because it's a fallacy. :-)
> >
> > Dave...
>
>I wrote the following program to test CHAIN vs. SETLL.  It did surprise me
>that CHAIN took only 13% more time.  That's not much difference.  Thank you
>for pointing out the not-so-obvious.
>
>      Ftestio    IF   E           K DISK
>
>      D myKey           S             12A   Dim(10000)
>      D i               S             10I 0
>      D Now             S               Z
>      D Then            S               Z
>      D Secs            S             10I 0
>
>       *-----------------------------------------------------------------
>
>      C                   For       i = 1 to 10000
>      C                   Read      testior
>      C                   Eval      myKey(i) = tikey
>      C                   EndFor
>
>       *-----------------------------------------------------------------
>
>      C                   Time                    Then
>      C                   For       i = 1 to 10000
>      C     myKey(i)      Setll     testio                                 70
>      C                   EndFor
>
>       *-----------------------------------------------------------------
>
>      C                   Time                    Now
>      C     Now           Subdur    Then          Secs:*MS
>      C     Secs          Dsply
>
>       *-----------------------------------------------------------------
>
>      C                   Time                    Then
>      C                   For       i = 1 to 10000
>      C     myKey(i)      Chain     testior                            70
>      C                   EndFor
>
>       *-----------------------------------------------------------------
>
>      C                   Time                    Now
>      C     Now           Subdur    Then          Secs:*MS
>      C     Secs          Dsply
>
>       *-----------------------------------------------------------------
>
>      C                   SetOn                                        LR
>      C                   Return
>
>Nathan M. Andelin
>www.relational-data.com
>
>
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