1. Explain the JVM architecture. I managed to explain about memory management including young generation old generation and string pools and how objects are reclaimed which I believe is exceptional for someone with just 3 years of experience. 2. You have a large file 1 GB and 100 MB RAM. How will you sort the file? - You can split the files into small chunks like 100 MB chunks and sort them 1 by 1 using technique like merge sort and keep this 10 files in the disk. Then you can use the merge process of merge sort(merge k arrays) and read the top lines from each file and output the smallest number to the target file. Still, he was looking for more optimization 3. How to get the middle element and delete the middle element from the stack in 0(1). I believe the question was meaningless as stack has only top pointer and size. But this question includes modifying the stack terminology where you maintain a pointer while forming a stack which was not specified in the question. What is tomorrow you ask me to get the 1/4th element in 0(1) then I should maintain another pointer? 4. How indexes are internally implemented in MongoDB database. I remember it was some form of a tree but was unable to recall the name. It is B+ tree.