Journal caching is quite helpful performance wise in an environment
- that has lots of "batch" processing, with lots of records updated
- in which the tables are journaled and commitment control is rarely if
ever used.

So while such an environment is often the result of turning on journally
for some HA product, it doesn't have to be.

I believe it was Rob Berendt @ Dekko who found the performance improvement
from turning on journal caching was much, much greater than the one he got
from moving from spinning disks to SSDs.


On Fri, Nov 19, 2021 at 5:42 PM Laurence Chiu <lchiu7@xxxxxxxxx> wrote:

We are about to go live with a system with two Power servers both running
IBM FlashSystes V5030 SANs fully populated with SSDs.

We are utilising Metro Mirror to keep our production and DR SANs in sync so
if production dies we can make our remote SAN LUN as writeable and IPL the
DR box.

Somebody mentioned to me be wary of journal caching turned on with the
command JRNCACHE(*YES) function in CHGJRN as you could have uncommitted
journals around when the system crashed and thus lose data. Another piece
of advice said you might only lose a few milliseconds of data in a worst
case sceario.

Given we don't have a high transaction volume system and the SANs are very
fast, it seems we could turn that feature off and not lose any performance
and also not lose any data. Does that seem like a reasonable option to
explore? Also it appears that journal caching is a paid option and since
this application is quite old and the configuration is not that well
documented, is there an easy way to tell if that option has been purchased
and is turned on?

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