Many good points. There is Journal Performance Redbook, but it is old, 2002.
Striving for Optimal Journal Performance on DB2 Universal Database for iSeries SG24-6286-00
I feel with the newer hardware, journaling as less impact than years ago.


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Buck Calabro
Sent: Thursday, February 20, 2014 9:23 AM
To: midrange-l@xxxxxxxxxxxx
Subject: Re: Need To Journal Files & System Impact

On 2/20/2014 6:23 AM, Jack Kingsley wrote:
I have a small group of files that I need to start to journal. Is
there a way to determine how journaling of these files would impact a system.
Example: How big the journal receiver will get, how many entries, CPU
overhead, should the objects be in the same library, etc. Was not
sure if there is a way to determine this or not.

No answers, but some questions that might help guide your thoughts.

I need to start to journal

Why? The point of this question is to determine if you are keeping before and after images or just after.

The journal receiver will be twice as large if you keep both images.
Countering that, you may not need to keep those journal receivers more than one backup cycle. In fact, you can let the system manage the receivers, and not keep hardly any at all on disk. Depending on why you are journalling...

How many entries? That depends on the applications that do updates. If you have a batch type application that touches every record once an hour, then you'll have (total file records * 24) entries per day. If you only touch 100 records a day, you'll have 100 journal entries per day.

CPU overhead... hm, not sure I'd worry about that unless you're journalling a multi-million row table that you touch every row continuously all day long. The journalling overhead on our system is very, very small even for the mega files.

I keep my journals & receivers in the same library. I only have one ASP here; not a big, complicated configuration. I find it easy to keep all the related pieces / parts together. Helps me maintain what little sanity I might have left.

There are lots of ways to go about this, and there probably isn't a single 'right' way. I've stumbled my way along and haven't seen any real hit on either disk or CPU. The list members with more complicated setups have seen what constitutes some 'wrong' ways. It will be interesting to hear their opinions.
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