Package org.apache.lucene.util.packed

Class MonotonicBlockPackedWriter

  • public final class MonotonicBlockPackedWriter
extends java.lang.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:
    MonotonicBlockPackedReader

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void add​(long l)
      Append a new long.
      void finish()
      Flush all buffered data to disk.
      long ord()
      Return the number of values which have been added.
      void reset​(DataOutput out)
      Reset this writer to wrap out.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • 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 Detail

      • add

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

      • reset

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

      • finish

        public void finish()
            throws java.io.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:
        java.io.IOException

      • ord

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