I found this issue after Discoverer CP9 upgrade.
The problem is – That in Discoverer Plus I can't drag an item to the Page Items section.In Discoverer Plus this action takes a lot of time or stacks the report forever.
In Discoverer Desktop it is done just fine .
The cause is that the Preference values for the 'MaxVirtualHeapMem' parameter is not picked up and the default value (which is small) is used. This results in a large amount of Disk I/O which results low performance of the application interface. Or 'MaxVirtualHeapMem' parameter is too small.
There is an Oracle document for this bug [ID 359124.1] for versions 10.1.2.48.18 or 10.1.2.50.05.
If you version is a higher and you stiil have this issue, you need to do the fiollowing:
1. Open the pref.txt in $ORACLE_HOME/discoverer/util.
2. Increase MaxVirtualHeapMem parameter.
3. Execute ./applypreferences.sh form $ORACLE_HOME/discoverer/util.
4. Recheck the issue.
Good Luck ..