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:

MonotonicBlockPackedReader

Constructor Summary

Constructors

Constructor and Description
MonotonicBlockPackedWriter(DataOutput out, int blockSize) Sole constructor.

Method Summary

Modifier and Type	Method and 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 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.