Quote:
Business users want the single page UI to be extremely fast and fluid. No lags.
I have to display 5,00,000 (5 hundred thousand/5 lac) records (Show names) in searchable Multi select drop down list.
The 2 sentences are contradictory, you can't have both at same time.
A drop down list of 500k lines will be also impractical to use. A drop down list with 500 lines is already difficult to use.
The multi select is a bad idea with 500k lines.
Quote:
What I have tried:
There is numerous ways to fail o, what you tried, It will be difficult to check what you done without code.
I would try to use a simple field with a drop down loaded as user type and a separate grid that hold all the selections.