PostgreSQL and MySQL both support compression of data, so even if you do not solve the duplicated key problem you still can reduce disk usage. The only benchma

PostgreSQL and MySQL both support compression of data, so even if you do not solve the duplicated key problem you still can reduce disk usage. The only benchmarks where I have seen MongoDB winning have been those where MongoDB was configured with different consistency requirements than MySQL and PostgreSQL. My suspicion is the MongoDB is slowest but I have never seen any high quality benchmarks.