I have two collections in MongoDB named colors and cities. Each collection has 150k documents. Both collections has a column called tracking_numbers. I need unique tracking numbers of colors collection that are not present in the cities collection. Actually I wrote the code in NodeJS using mongoose, it is taking few seconds for finding unique tracking numbers for smaller collection, but when it comes to large collection (say for 150k documents) it is taking more time. Please provide me the solution for speeding the process.
This is the code that I wrote.
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