RE: Positioning the Cursor, from the Toolbox

Yeah, a lot of us know the answer.  Sometimes we don't have time to
immediately respond in the list, though <smile>.

I've done extensive work with the RLA methods (I've even written a for-fee
lab on the subject which explains how RLA compares to JDBC for file access).
I can definitively say the following:

1. The AS400KeyedFile allows keyed access ALMOST exactly like you would
expect in standard native I/O, including partial key access.  There is a
subtle difference in that the "cursor" for RLA is effectively "on" a given
record, where with native I/O it is effectively "between" records.  It
really only makes a difference when you're switching directions during
sequential-by-key processing.

2. I've never run into any performance issues opening a keyed file.  I have
no idea who wrote that statement; there's a good chance that they were
dealing with a file with MAINT(*DELAY) on the access path.  Note that they
talk about opening a KeyedFile over a physical; they don't seem to
understand the concept of a logical file (I suspect that if you tried to
open a KeyedFile over a physical with no keys, it would fail). 

These performance hints are written by people who are more familiar with
Java than the iSeries.  For example, another hint on the same page says:

"Specify a CCSID of 13488 for any of your text fields in your physical file.
CCSID 13488 is Unicode, so when data is read and written between Java and
i5/OS, little if any text conversion needs to be done. Most text fields in a
physical file (for an English system) default to 37 - the English EBCDIC
CCSID. Data translation occurs between this CCSID and Unicode since all Java
characters and Strings are in Unicode. Character conversion can become a
serious bottleneck for applications that handle large amounts of string d
data."

Heee! In order to make your Java programs faster, just double your disk
usage!  So, take the hints with a grain of salt.  If you'd like to know for
certain about the open time, I'd suggest a very simple program: create a
KeyedFile over your largest logical view, then open it and read a record.

Joe

From: James H H Lampert

"Joe Sam Shirah" <joe_sam@xxxxxxxxxxxxx> wrote:

   However, my understanding is that your assumption
regarding sequential-by-key access is incorrect.  In the
KeyedFile javadoc it says "Access the records in an AS/400
file sequentially or by key."  Secondly,
note that the methods you refer to come from AS400File
and are not overridden in KeyedFile.

That the methods aren't overridden says nothing
conclusive: presumably the methods aren't doing the actual
record fetches; rather, there's an ODP somewhere doing
them. Moreover, while KeyedFile doesn't override the
AS400File methods (at least not openly), neither does it
introduce any new methods for sequential-by-key
processing.

An empirical determination would certainly be possible,
but would be rather time-consuming and inconvenient, given
that we don't use a lot of Toolbox access around here.

DOES ANYBODY ELSE KNOW THE ANSWER?!?