Implements a fast key/value database to store the metrics gathered to create the session summary event. The store is buffered in memory until it is flushed to disk by callingFlush(). It is not designed to handle millions of key/value pairs, but rather a small subset that fits in memory. The implementation reserve disk space ahead of time and can usually perform in-place update. Setting or getting intrinsic types (int32, uint32, int64, uint64, float, double, bool as well asFDateTime) doesn't allocate memory. The string time is often updated in place if enough capacity was reserved. All store operations are thread safe and atomic from the caller perspective.