RE: [IE] Re: Mirroring by RRN slow for large file -- MIDRANGE-L

Thanks Augie,

We ensure that there are no batch jobs on the apply side that use much CPU. Any jobs that do run are mostly read only an any updates are to non-journalled files.
Most of the time the only thing running is iTera replication.

All access paths are *immed. There is no EDTRDBAP object and I've never seen any access path rebuilding occurring.
Yes, there has been a virtual role swap about a year back when we never noticed this latency.

The large files were changed to *SSD storage a few months back but that should only improve things.
We don't have SSD on the apply system. The large file in question has storage unit *ANY there.
I've just noticed that, of the 16 files that are in SSD on the source system, 6 of them also had *SSD on the apply system. Not sure if that matters but they're all now *ANY on the apply system.

Regards, Peter

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Augie Palumbo
Sent: Monday, 14 August 2017 6:25 AM
To: Midrange Systems Technical Discussion
Subject: [IE] Re: Mirroring by RRN slow for large file

Hi Pete,

Generally speaking the only time you should see latency on the apply side
is:

Resources. CPU/Memory
iTera was down for a time
Commitment Control
Locking of files - i.e other jobs running on the target for perhaps read only functions Large batch job generating many transactions in a short time.

The latency of data on the apply side shouldn't be happening but it nothing to do with RRN processing vs keyed. I assume all of the access paths are are *IMMED for update and none of them ate *DELAY.

EDTRBDAP will tell you if the system is rebuilding access paths. If it is this would cause a transaction to queue but only until the access path was re-built. Once it was then it should fly threw the data. I've seen upwards of billions of transactions a day and no latency.

Has this always happened? Was there an event that may have caused this?
Have you ever done a role swap? or even a virtual role swap?

Product like iTera have been out for over 25 years now and have proven methods of applying data. I suspect there is something else happening that is causing the delay..

Thanks
Augie

Augie Palumbo
312-735-3723
702-826-2836

On Sun, Aug 13, 2017 at 8:02 AM, Nathan Andelin <nandelin@xxxxxxxxx> wrote:

Peter,

I haven't actually tested the performance of RRN vs. keyed index
access on IBM i, but the IBM i index search may actually return a RRN
if it works like some of the other DBMS products I've worked with. So
a known RRN may be the quickest way to find records.

I'm not that familiar with iTera, but I wonder if it may have a
configuration setting that controls the queue on the target system?

Nathan.

On Sat, Aug 12, 2017 at 11:39 PM, Peter Connell
<Peter.Connell@xxxxxxxxxxx

wrote:

I assume that mirroring software (ITERA) that uses journals for
replication to another IBM i5 performs updates and deletes on the
target system by using the RRN stored in each journal to replicate
the update or delete.
This is a reasonable assumption since the mirroring software knows

nothing

about any index it might use to achieve the update of delete via an

access

path.

A large file on the source system of 170 million records which may

attract

several million updates and deletes in a day results in these being

queued

for long periods on the target system before the actual replication
event occurs to keep the file in synch.
I presume that the substantial latency observed between the source
and target updates and deletes is because the record be updated or
deleted is being located via RRN.
Perhaps this is because DB2 has to do a table scan to find the
record which is slower than an update via a unique index.

It's not clear if creating an index whose primary key is RRN would
help otherwise the only solution may be to do a custom replication
that reads the journal, and extracts the unique index to do an update or delete.

Regards, Peter

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