Package org.apache.lucene.util.packed

Class MonotonicBlockPackedWriter

java.lang.Object
org.apache.lucene.util.packed.MonotonicBlockPackedWriter
public final class MonotonicBlockPackedWriter extends Object
A writer for large monotonically increasing sequences of positive longs.

The sequence is divided into fixed-size blocks and for each block, values are modeled after a linear function f: x → A × x + B. The block encodes deltas from the expected values computed from this function using as few bits as possible. Each block has an overhead between 6 and 14 bytes.

Format:

  • <BLock>BlockCount
  • BlockCount: ⌈ ValueCount / BlockSize ⌉
  • Block: <Header, (Ints)>
  • Header: <B, A, BitsPerValue>
  • B: the B from f: x → A × x + B using a variable-length long
  • A: the A from f: x → A × x + B encoded using Float.floatToIntBits(float) on 4 bytes
  • BitsPerValue: a variable-length int
  • Ints: if BitsPerValue is 0, then there is nothing to read and all values perfectly match the result of the function. Otherwise, these are the zigzag-encoded packed deltas from the expected value (computed from the function) using exaclty BitsPerValue bits per value
See Also:

  • Constructor Details

    • MonotonicBlockPackedWriter

      public MonotonicBlockPackedWriter(DataOutput out, int blockSize)
      Sole constructor.
      Parameters:
      blockSize - the number of values of a single block, must be a power of 2

  • Method Details

    • add

      public void add(long l) throws IOException
      Append a new long.
      Throws:
      IOException

    • reset

      public void reset(DataOutput out)
      Reset this writer to wrap out. The block size remains unchanged.

    • finish

      public void finish() throws IOException
      Flush all buffered data to disk. This instance is not usable anymore after this method has been called until reset(DataOutput) has been called.
      Throws:
      IOException

    • ord

      public long ord()
      Return the number of values which have been added.