RE: SQL Deterministic UDF and File Read Count

Huh?

Not sure I understand your question.  Are you saying that you've called the 
function multiple times, but the access count for the file only shows one 
call's worth of I/O?

That would make sense since you defined the function as deterministic.

The manual states that deterministic "Specifies that the function will always 
return the same result from
successive invocations with identical input arguments."

As I understand it, with a deterministic function, OS/400 may cache the prior 
value and just return it instead of actually calling the function again.  This 
would appear to be what you are seeing.  If you're not seeing it, it may be 
that OS/400 decided not to cache the results.

Note that I don't think there's any way to know how long OS/400 keeps this 
cached value around.  I assume it isn't permanent.

However, be very careful specifying DETERMINISTIC.  I tend to specify 
deterministic only for functions that don't access files.  Such as a date 
conversion routine.  With a function that access a file, it would be too easy 
for a change to the file not to affect the result of the function when it 
should have.

HTH,


Charles Wilt
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
 

> -----Original Message-----
> From: midrange-l-bounces@xxxxxxxxxxxx
> [mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of Bill
> Sent: Tuesday, February 15, 2005 12:40 PM
> To: Midrange List
> Subject: SQL Deterministic UDF and File Read Count
> 
> 
> I have created an SQL UDF which is specified as 
> Deterministic.  The UDF is
> written in RPGLE and accesses a table as part of it's logic.  
> When I do a
> Select statement in SQL and reference the UDF it returns the data as
> expected.
> 
> The concern I have is regarding the file access count:  it 
> has the same
> number of accesses as there are number of records returned -- 
> but the input
> parameters to the UDF were the same for each UDF access.
> 
> Am I correct that there would be one access to the UDF's table
> corresponding to the first "call" and then since each 
> subsequent call has
> the same parameter values it shouldn't access the table 
> again?   This is on
> a V5R2 system.
> 
> Bill
> 
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