I am trying to create a crowd-sourcing project in which I would like people to sense data using their Raspberry Pi. I am currently using MySQL to push data from a Java program running on Raspian after every value is read. Although using this technique, I might lose some values if the connection is lost.
Instead I wish to store the data on a local DB on raspberry pi which would send/sync its data with the main SQL server every 30 minutes. But my problem is that I want this main DB to synced up with multiple local DBs of the various Raspberry Pi being used for crowd sourcing.
I would really grateful if someone could suggest me a detailed architecture and technique for the same.