Re: Possible timing issue with IO

Roger,

You're remembering...but the "dirty bit" is in the DB.

The problem here is that RPG does it's own buffering, so the DB doesn't yet
know the record has been added. FEOD(N) forces RPG to flush it's buffers
to the DB.

http://www-01.ibm.com/support/docview.wss?uid=nas8N1018493

Charles


On Fri, Jan 24, 2014 at 5:18 PM, Roger Harman <roger_harman@xxxxxxxxxxx>wrote:

I always thought there was a "dirty bit" set when a record is added/changed
to avoid such an issue.

Am I recalling something about this incorrectly? (Obviously so, it would
seem)



-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Vernon Hamberg
Sent: Friday, January 24, 2014 2:04 PM
To: RPG programming on the IBM i (AS/400 and iSeries)
Subject: Re: Possible timing issue with IO

Thanks much - this confirms what we are seeing.

Ah the pain of needing immediate visibility!!

Vern

On 1/24/2014 3:52 PM, Jon Paris wrote:

The difference between FEOD and FEOF(N) is that in the former case your

program is suspended until the data makes it all the way onto the physical
disk (or at least the drive's cache I guess). When you use the (N) extender
you are telling the OS that you are happy to rely on the content of its
buffers and don't actually need the data to be forced to the actual disk.
The speed differences are significant. You'll barely notice FEOD(N) but you
will notice FEOD.

On 2014-01-24, at 4:26 PM, Vernon Hamberg <vhamberg@xxxxxxxxxxxxxxx>

wrote:

hi Eric

That seems the likely suspect. If things are not out of the buffer,
then DB management knows nothing about them, and the logicals won't
be maintained, right?

Have you used the N extender on FEOD? Reference says that unwritten
from a block get writ to database, although not necessarily to disk.
So things should be available, I'd think.

Index maintenance is a part of this, maybe, although a request for a
record know to DB should just make the program wait until maintenance
is done, as I recall.

Thanks much!
Vern

On 1/24/2014 3:19 PM, DeLong, Eric wrote:

Vernon,

I'd suspect that you have data written to buffer that has not been

flushed to disk yet. You could try issuing a FEOD to the file before
exiting.

-Eric DeLong

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Vernon Hamberg
Sent: Friday, January 24, 2014 3:17 PM
To: RPG programming on the IBM i / System i
Subject: Possible timing issue with IO

Y'all

I haven't had to deal with quirky IO issues in a long time, so here
goes with my problem - hope someone has seen this behavior.

I have a program that reads through a file (let's call it VHFILE)
from a certain position and is checking for duplicates of a type -
not important - I'm using a state machine to handle this.

When this program is called on its own, it finds the duplicates.

When it is called from a program that just wrote to the file in
question, it rarely finds anything - but it does sometimes catch 1
or 2 instances of the problem.

It seems that this new program doesn't see the data that was just

written.

VHFILE has 3 logicals - and VHFILE is quite large - one of what we
call our big files.

VHFILE - arrival - 51million
VHFILEA - 51million entries - 1.5GB
VHFILEB - 51million entries - 1.8GB
VHFILEC - 10million entries (S/O) - 420MB

OK, here's more info on the call stack -

1. CLPGMA - OPM
calls
2. CLPGMB - OPM with simple OVRDBF on file in question
calls
3. RPGPGMA - ILE - *CALLER - uses VHFILEA as UF A
(update +
add) and has deletes and writes
calls (after all writes are done - the number varies,

)

4. CLPGMC - ILE - *DFTACTGRP
calls
5. RPGPGMB - ILE - QILE - uses VHFILEC as UF
(update only) and has only deletes

There is no need of sharing ODPs.

I recognize the "flaky" activation group structure, but I don't
think it should matter - in fact, it might help, to isolate opening
VHFILEC from the open of VHFILEA.

No commitment control in place - there is iTera for replication or

whatever.

So -

1. Is FEOD a way to overcome this?
2. And is the N extender useful? RPG Reference says it can perform
better - unwritten records in a block are written to the database,
although not necessarily to disk (non-volatile storage).

Or some other idea.
Thanks
Vern

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www.partner400.com
www.SystemiDeveloper.com

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