Hi, I'm not sure what 'we can able to fetch 5lacks records in single load' means. Could you explain what problem you encounter? If it is that you run out of memory on the SAP BW server because you are extracting to much data in the BEx query you need to use or add a variable in the BEx query that limits the amount of data you are extracting. If you have no experience in SAP BW you will not be able to add a variable or modify the BEx query. You could also extract data directly from the InfoProvider by using the Qlik SAP InfoProvider connector that is built differently and does not consume that much memory on the BW server.
You are not able do modify any MDX manually (and the BEx connector is not using the MDX interface, that is the OLAP connector).
If you want to limit the data you extract with a BEx query the BEx query needs to have 'Query Variables' (defined in SAP BEx Query Designer or HANA Studio if BW Query). In my example you can filter on a date range so set the date range so in that case you need to set the date range so that the result set is small enough for your BW Application server to handle. If you don't have 'Query Variables' in your select dialog in Sense you need to talk to someone who can add a variable to the BEx query:
If you have historical data that does not change you can store that away in a qvd that you load from when reloading the app to limit the reload time. And then combine that historical data with more recent SAP BEx extractions.