/*
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 Mar 17, 2009
*/
package com.bigdata.sparse;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import org.apache.log4j.Logger;
import com.bigdata.btree.ISimpleSplitHandler;
import com.bigdata.btree.IndexSegment;
import com.bigdata.util.BytesUtil;
/**
* This class imposes the constraint that the separator key must not split a
* logical. This constraint is required in order for the logical row store to
* retain its row-wise ACID semantics when there is more than one shard for that
* row store. This is done using a linear scan forward from the recommended
* splitAt index until the first tuple is identified which would be part of a
* different logical row. The index of that tuple is returned.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class LogicalRowSplitHandler implements ISimpleSplitHandler, Externalizable {
/**
*
*/
private static final long serialVersionUID = 9180840621078374197L;
protected static transient final Logger log = Logger
.getLogger(LogicalRowSplitHandler.class);
public static transient final ISimpleSplitHandler INSTANCE = new LogicalRowSplitHandler();
public byte[] getSeparatorKey(final IndexSegment seg, final int fromIndex,
final int toIndex, final int splitAt) {
final byte[] a = seg.keyAt(splitAt);
final int alen = new KeyDecoder(a).getPrefixLength();
for (int i = splitAt + 1; i < toIndex; i++) {
final byte[] b = seg.keyAt(i);
final int blen = new KeyDecoder(b).getPrefixLength();
/*
* Compare the first N bytes of those keys (unsigned byte[]
* comparison).
*/
final int cmp = BytesUtil.compareBytesWithLenAndOffset(//
0/* aoff */, alen, a,//
0/* boff */, blen, b//
);
// the keys must be correctly ordered.
assert cmp <= 0;
if (cmp < 0) {
/*
* The N byte prefix has changed. Clone the first N bytes of the
* current key and return them to the caller. This is the
* minimum length first successor of the recommended key which
* can serve as a separator key without breaking the logical
* row.
*/
final byte[] prefix = new byte[blen];
System.arraycopy(b/* src */, 0/* srcPos */, prefix/* dest */,
0/* destPos */, blen/* length */);
if (log.isInfoEnabled())
log.info("Found: prefix=" + BytesUtil.toString(prefix)
+ ", splitAt=" + splitAt + ", i=" + i);
return prefix;
}
}
log.warn("No successor: splitAt=" + splitAt);
// No such successor!
return null;
}
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
// NOP
}
public void writeExternal(ObjectOutput out) throws IOException {
// NOP
}
}