The document summarizes a study on protecting user privacy when querying encrypted databases. It first describes how an adversary can infer information about user queries by monitoring I/O activity, even with an encrypted database and B+ tree. It then proposes a PB+ tree index that conceals the order of leaf nodes to prevent the adversary from determining the exact nodes or query ranges accessed. Finally, it notes that PB+ tree balances privacy and computational overhead, and experiments show it effectively impairs the adversary's ability to learn the B+ tree structure or query ranges in different scenarios.