com.bigdata.bop.ap

Class SampleIndex.BitVectorOffsetSampler

java.lang.Object

com.bigdata.bop.ap.SampleIndex.BitVectorOffsetSampler

All Implemented Interfaces:

SampleIndex.IOffsetSampler

Enclosing class:

SampleIndex<E>

public static class SampleIndex.BitVectorOffsetSampler
extends Object
implements SampleIndex.IOffsetSampler

Return a randomly selected ordered array of offsets in the given half-open range.

This approach is based on a bit vector. If the bit is already marked, then the offset has been used and we scan until we find the next free offset. This requires [rangeCount] bits, so it works well when the rangeCount of the key range is small. For example, a range count of 32k requires a 4kb bit vector, which is quite manageable. FIXME There is something broken in this class, probably an assumption I have about how LongArrayBitVector works. If you enable it in the stress test, it will fail.

Constructor Summary

Constructors

Constructor and Description
SampleIndex.BitVectorOffsetSampler()

Method Summary

Methods

Modifier and Type	Method and Description
long[]	getOffsets(long seed, int limit, long fromIndex, long toIndex) Return an array of tuple indices which may be used to sample a key range of some index.

Methods inherited from class java.lang.Object

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

Constructor Detail

SampleIndex.BitVectorOffsetSampler

public SampleIndex.BitVectorOffsetSampler()

Method Detail

getOffsets

public long[] getOffsets(long seed,
                int limit,
                long fromIndex,
                long toIndex)

Return an array of tuple indices which may be used to sample a key range of some index.

Note: The caller must stop when it runs out of offsets, not when the limit is satisfied, as there will be fewer offsets returned when the half open range is smaller than the limit.

Note: The utility of this class is limited to smaller range counts (32k is fine, 2x or 4k that is also Ok) so it will reject anything with a very large range count.

Specified by:

getOffsets in interface SampleIndex.IOffsetSampler

Parameters:

seed - The seed for the random number generator -or- ZERO (0L) for a random seed. A non-zero value may be used to create a repeatable sample.

limit - The maximum #of tuples to sample.

fromIndex - The inclusive lower bound.

toIndex - The exclusive upper bound0

Returns:

An array of at most limit offsets into the index. The offsets will lie in the half open range (fromIndex,toIndex]. The elements of the array will be in ascending order. No offsets will be repeated.

Throws:

UnsupportedOperationException - if the rangeCount is GT Integer.MAX_VALUE