Hello,
I have written many tools to parse JSON-encoded data, and other tools that require low-latency database updates, so I think I have all the skills needed to solve this problem.
Depending on the volumes of data involved, I would probably choose Python for the JSON decoding (the cJSON Python library is implemented in C, making it extremely efficient), and for a database I would suggest LevelDB, a very speedy key-value database.
As a newcomer to freelancer, I've entered a low bid to try to offset my lack of reputation, but I do feel that I can provide a complete and optimal solution for the task.
Thanks!
Rob