July 25, 2016

nildb: a memory-efficient key/value database


NIL Key/Value database

NILDB is about the simplest key/value store you'll ever see, anywhere. It's written in plain vanilla C using only the standard string and FILE I/O functions, and should port to just about anything with a disk or something that acts like one.

NILDB is based on KISSDB, with significant update to reduce file size and improve efficiency, and also added the capability to delete entries.

It stores keys and values of fixed length in a stupid-simple file format based on fixed-size hash tables. If a hash collision occurrs, a link list is created and the entry is appended to the database. You can add, update, lookup and delete.

  • Tiny
  • Almost zero memory footprint
  • Very space-efficient on disk
  • Pretty respectably fast, especially given its simplicity
  • 64-bit file size limit is 2^64 bytes, and 2^32 offset limit between the same hashed entries.
  • Ports to anything with a C compiler and stdlib/stdio
  • Public domain
  • Works cross big-endian and little-endian system.
  • Fixed-size keys and values, must recreate and copy to change any init size parameter (Although can be adapted to varied value size easily)
  • No search for subsets of keys/values
  • No indexes
  • No transactions
  • No special recovery features if a database gets corrupted
  • No built-in thread-safety (guard it with a mutex in MT code)
  • No built-in caching of data (use filesystem cache)
Alternative key/value stores and embedded databases:
  • KISSDB The base of this project, uses multiple hash tables instead of just one
  • MDB uses mmap() and is very fast (not quite as tiny/simple/portable)

NILDB is in the public domain as according to the Creative Commons Public Domain Dedication.