Performance Tuning and upgrade of Ops Center

Our Ops center is currently on version 7.5.0.7 and having DB of around 18GB.

We are having issues while defrag of DB. It always took ages to complete and most of the time it get failes while reload.

Below is the content of server.conf file.

-n OPSCENTER_hostname -x tcpip(LocalOnly=YES;BROADCASTLISTENER=0;DOBROADCAST=NO;ServerPort=13786;) -gd DBA -gk DBA -gl DBA -gp 8192 -ti 0 -c 256M -ch 1024M -cl 256M
-zl -os 1M -m

Kindly suggest what values need to be changed considering the DB of 18GB. Also about heap size.

Also we are planning to upgrade it to next version. Please suggest to what version we need to upgrade it too and what will be upgraded procedure for the same.