/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Sep 30, 2010
*/
package com.bigdata.bop.cost;
import java.io.Serializable;
import com.bigdata.btree.IndexSegment;
/**
* A cost model for a range scan on an {@link IndexSegment}.
* <p>
* Note: This uses a summary description of the {@link IndexSegment} for the
* cost model. This makes sense because we generally have 100s of index segments
* in scale-out and we do not want to probe them all for their exact costs.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class IndexSegmentCostModel implements Serializable {
/**
* @todo should be either Externalizable and explicitly managed versioning
* or Serializable with a public interface for versioning.
*/
private static final long serialVersionUID = 1L;
private final DiskCostModel diskCostModel;
/**
*
* @param diskCostModel
* The disk cost model.
*/
public IndexSegmentCostModel(final DiskCostModel diskCostModel) {
if (diskCostModel == null)
throw new IllegalArgumentException();
this.diskCostModel = diskCostModel;
}
/**
*
* @param rangeCount
* The range count for the index scan.
* @param branchingFactor
* The branching factor for the index segments for this scale-out
* index.
* @param averageBytesPerLeaf
* The average #of bytes per leaf for this scale-out index.
* @param xferBufferSize
* The size of the disk transfer buffer.
*
* @return The estimated time for the range scan (milliseconds).
*/
public double rangeScan(final int rangeCount, final int branchingFactor,
final int averageBytesPerLeaf, final int xferBufferSize) {
if (rangeCount == 0)
return 0d;
if (xferBufferSize == 0)
throw new IllegalArgumentException();
// One seek per leaf.
final double averageSeekTime = diskCostModel.seekTime;
// Expected #of leaves to visit.
final int expectedLeafCount = (int) Math.ceil(((double) rangeCount)
/ branchingFactor);
// Expected #of bytes to transfer.
final int leafBytesToXFer = expectedLeafCount * averageBytesPerLeaf;
// Expected #of disk transfers.
final int xfers = (int) Math.ceil(((double) leafBytesToXFer)
/ xferBufferSize);
// Expected transfer time (ms).
final double xferTime = leafBytesToXFer
/ (diskCostModel.transferRate / 1000);
// Expected disk seek time (ms).
final double seekTime = averageSeekTime * xfers;
// Expected total time (ms).
final double totalTime = seekTime + xferTime;
return totalTime;
}
}