i implemented a ListModel with cache and used with autopaging feature as documented:

https://www.zkoss.org/wiki/ZK%20Developer's%20Reference/Performance%20Tips/Listbox,%20Grid%20and%20Tree%20for%20Huge%20Data/Implement%20ListModel%20and%20TreeModel

but when i got to have a totaSize of 1.7 milion record the listbox hang like forever, even if my custom listbox loaded 50 of them and shows only 20 of them!

using jvisual vm i discovered that Listbox just create totalSize of Listitem then Iterate through them all!!!

then i discovered someone else fuond this scalability bug and was forced to to manual paging!
https://www.zkoss.org/wiki/Small_Talks/2015/December/custom_database_paging_listbox

i even tried Rended On Demand... with no luck, even with ZK EE
https://www.zkoss.org/wiki/ZK%20Developer's%20Reference/Performance%20Tips/Listbox,%20Grid%20and%20Tree%20for%20Huge%20Data/Turn%20on%20Render%20on%20Demand

just create pageSize of Listitem then reuse it when page change!