DataDraw is an ultra-fast persistent database for high performance programs
written in C. It's so fast that many programs keep all their data in a
DataDraw database, even while being manipulated in inner loops of compute
intensive applications. Unlike slow SQL databases, DataDraw databases are
compiled, and directly link into your C programs. DataDraw databases are
resident in memory, making data manipulation even faster than if they were
stored in native C data structures (really). Further, they can automatically
support infinite undo/redo, greatly simplifying many applications.

DataDraw databases can be persistent. Modifications to persistent data are
written to disk as they are made, which of course dramatically slows write
times. However, DataDraw databases can also be volatile. Volatile databases
exist only in memory, and only for the duration that your program needs it.
Volatile databases can be directly manipulated faster than C structures,
since data is better organized in memory to optimize cache performance.
DataDraw supports modular design. An application can have one or more common
persistent databases, and multiple volatile databases to support various
tools' data structures. Classes in a tool's database can extend classes in
the common database. DataDraw is also 64-bit optimized, allowing programs to
run much faster and in less memory than standard C programs using 64-bit
pointers. This is because DataDraw databases support over 4 billion objects
of a given class with 32-bit object references.

WWW: http://datadraw.sourceforge.net/