Package org.apache.lucene.util.packed

Class BlockPackedWriter

  • public final class BlockPackedWriter
extends java.lang.Object
    A writer for large sequences of longs.

    The sequence is divided into fixed-size blocks and for each block, the difference between each value and the minimum value of the block is encoded using as few bits as possible. Memory usage of this class is proportional to the block size. Each block has an overhead between 1 and 10 bytes to store the minimum value and the number of bits per value of the block.

    Format:

    • <BLock>BlockCount
    • BlockCount: ⌈ ValueCount / BlockSize ⌉
    • Block: <Header, (Ints)>
    • Header: <Token, (MinValue)>
    • Token: a byte, first 7 bits are the number of bits per value (bitsPerValue). If the 8th bit is 1, then MinValue (see next) is 0, otherwise MinValue and needs to be decoded
    • MinValue: a zigzag-encoded variable-length long whose value should be added to every int from the block to restore the original values
    • Ints: If the number of bits per value is 0, then there is nothing to decode and all ints are equal to MinValue. Otherwise: BlockSize packed ints encoded on exactly bitsPerValue bits per value. They are the subtraction of the original values and MinValue
    See Also:
    BlockPackedReaderIterator, BlockPackedReader

    • 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

      • BlockPackedWriter

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

    • Method Detail

      • reset

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

      • add

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

      • 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.