Bit-Arrays are much-useful and quite-fast data-structure that have a variety of uses. One of the most important ones in context of Big-Data is the use in Bloom filters. To store the bloom we need a very fast bit-array and the ones that can be persisted as well. Java has only an in-memory bit-array implementation. I needed a file-persisted one to be used in conjunction with the bloomfilter filter project. Thus, I added the following implementations to the jerry-core project.

  • FastBitArray - an implementation that is much faster than the standard Java implementation
  • FileBackedBitArray - backed by file persistence, and all operations are flushed back automatically
  • MMapFileBackedBitArray - one that is file-persisted, but uses memory-mapped files for nuch faster performance
  • JavaBitSetArray - one that uses internal Java implementation underneath

Usage is pretty simple as,

final int maxElements = 1000 * 1000; // 1 million
BitArray ba = new FileBackedBitArray(new File(""), maxElements);

boolean updated = ba.setBit(13); // returns true
updated = ba.setBit(13); // returns false
udpated = ba.setBit(13); // returns true

boolean isSet = ba.getBit(13); // returns true

// using the memory-mapped version is similar
ba = new MMapFileBackedBitArray(new File("my-bit-array"), maxElements);

// all other operations are the same

I have used MMapFileBackedBitArray in production for the last few years and has been quite useful and fast.

Hope this helps.