Re: Question on file I/O optimization (in a "nightly refresh" program that currently takes all night AND ALL DAY)

James,

If you want to really improve performance, use SQL to insert the rows as a set.

Caveats:
- Destination file shouldn't be journaled
- If destination file is journaled, see if HA Journal Performance
(5722-SS1 option 42) is installed and "journal caching" can be used
- If neither of the above is true, you'll want to use commitment
control and batch read/write rows with periodic commitments.

Actually, the above caveats apply to RLA from RPG also....

The best way to do this with RPG would be to read from a logical file
that contained just the 11 fields you are interested in.

Assuming you RPG RLA is in arrival sequence (or your on 6.1 or higher)
, you could use an SQL view in place of the logical.

HTH,
Charles


On Tue, Oct 26, 2010 at 1:31 PM, James H. H. Lampert
<jamesl@xxxxxxxxxxxxxxxxx> wrote:

Comparing old-style RPG reads from externally-described files (i.e., a
target DS may not be specified at all) to the new option of specifying a
target DS that's defined on the file:

When I first learned of the new option, I was told that it was more
efficient, because it replaces a whole bunch of individual field data
transfers with one big blit of the entire record.

The file in question (opened for input only) has 314 fields. But we are
only looking at 11 of those fields, and 7 of them are currently defined
in 2 other structures, and in one of those, it effectively makes fields
that are non-contiguous in the file contiguous in the structure the
program refers to.

I started looking into converting this to the new "read-to-DS," but then
I realized that I might be barking up the wrong tree, replacing implicit
individual field transfers with explicit ones, and/or replacing
comparisons of entire structures with comparisons of the individual
fields therein.

The obvious question is whether or not RPG, when doing an old-style
externally-described read, skips the fields that are never referenced,
or transfers them anyway.

So am I barking up the wrong tree here?

--
JHHL
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