RE: performance loading a subfile

Booth Martin wrote:

>With no filter set the subfile loads 
>quickly and happily.  However if the 
>user chooses to filter out  99.5% 
>of the records then loading the 10 
>records may take thousands of 
>reads to find 10 that pass.  In this 
>case the performance is dreadful.  

It sounds like you are doing a READ followed by a compare to see if the
record is desirable.  The system has to find the record, move it to a
machine buffer, move it to the RPG buffer, map the record into each field,
do the comparison and discard the lot.  That hurts.  

You want to move toward reducing the I/O load.  Some thoughts:

1) Use OPNQRYF to do the selection.
2) Use SQL to make the selection.
3) Use the minimum number of fields.
4) Define logical files so that you can always do SETLL/READE.
5) Have your program recognise the bad performing filter and read
sequentially using a large blocking factor.

What fits best depends on how much work you want to do to accommodate the
bad performer.  You may settle on a combination.  The idea is to:

a) Reduce the number of records you read in RPG.  The database is MUCH more
efficient at filtering records.
b) Reduce the record length of records you read in RPG.  The fewer fields,
the fewer mapping operations.
c) Use Blocked I/O - the system can keep that buffer full before your RPG
program needs a record.

To more directly answer your original question, change your display file to
FRCWRT(*YES) and every time you load a record into the subfile, WRITE the
control record.  The screen will display the (now longer) subfile.  

If you find that you need to interrupt the load process, you'll need to add
INVITE and a data queue to the display file.  Check the data queue after
each database READE. and put your interrupt logic there.

Buck Calabro
Aptis; Albany, NY
"We are what we repeatedly do.
 Excellence, then, is not an act, but a habit." --Aristotle


Billing Concepts Corp., a NASDAQ Listed Company, Symbol: BILL
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