是否有数据存储，我可以通过数组索引而不是哈希键直接访问数据？ Redis的？ MongoDB的？

I need an external C/C++ memory efficient (!) data storage for a Java app which does not have the downside of a normal database lookup (b tree) but which uses my IDs as array index. Is there an open source solution for this? I implemented this in C++ in-memory only, but I would like to have a "storage to disc" option in case of a crash or for backup. Also Java binding would be cool.I need an external C/C++ memory efficient (!) d