message system in android app and web using php, javascsript

can anyone give me an idea on what to do. I'm doing a student portal system using android app and web. I have message feature wherein the teacher can send message to student. what am i going to use for storing messages. I'm afraid that if i use database it might slow the system. the android app and web must link together. the teacher can use the app to send message and the student can view it on web. thanks