This object store abuses mmap and tries to avoid your GC at the same time, so large databases can exist on disk and not use up all of your available memory? Depends on your mmap implementation but it is still interesting.
http://cl-www.msi.co.jp/projects/manardb/index.html
Efficiency
According to our benchmarks, when instantiating a object with two slots one million times, manardb is about seven times faster than AllegroCache 2.1.11 on Allegro 8.1, and about fifteen times faster than AllegroCache on SBCL 1.0.31. It is more than ten times faster to iterate over the 1M objects created and sum the values of one numeric slot on Allegro Lisp, and about one hundred times faster on SBCL.
Portability
It uses the mremap system call so is restricted to Linux. It would be trivial to change the mremap to a munmap, followed by mmap on other UN*X like platforms, as manardb is already prepared for the base address of the mapping to change.
abram