org.iq80.leveldb.table.BlockIterator Maven / Gradle / Ivy
/**
* Copyright (C) 2011 the original author or authors.
* See the notice.md file distributed with this work for additional
* information regarding copyright ownership.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.iq80.leveldb.table;
import com.google.common.base.Preconditions;
import org.iq80.leveldb.impl.SeekingIterator;
import org.iq80.leveldb.util.SliceInput;
import org.iq80.leveldb.util.Slice;
import org.iq80.leveldb.util.Slices;
import org.iq80.leveldb.util.VariableLengthQuantity;
import org.iq80.leveldb.util.SliceOutput;
import java.util.Comparator;
import java.util.NoSuchElementException;
import static org.iq80.leveldb.util.SizeOf.SIZE_OF_INT;
public class BlockIterator implements SeekingIterator
{
private final SliceInput data;
private final Slice restartPositions;
private final int restartCount;
private final Comparator comparator;
private BlockEntry nextEntry;
public BlockIterator(Slice data, Slice restartPositions, Comparator comparator)
{
Preconditions.checkNotNull(data, "data is null");
Preconditions.checkNotNull(restartPositions, "restartPositions is null");
Preconditions.checkArgument(restartPositions.length() % SIZE_OF_INT == 0, "restartPositions.readableBytes() must be a multiple of %s", SIZE_OF_INT);
Preconditions.checkNotNull(comparator, "comparator is null");
this.data = data.input();
this.restartPositions = restartPositions.slice();
restartCount = this.restartPositions.length() / SIZE_OF_INT;
this.comparator = comparator;
seekToFirst();
}
@Override
public boolean hasNext()
{
return nextEntry != null;
}
@Override
public BlockEntry peek()
{
if (!hasNext()) {
throw new NoSuchElementException();
}
return nextEntry;
}
@Override
public BlockEntry next()
{
if (!hasNext()) {
throw new NoSuchElementException();
}
BlockEntry entry = nextEntry;
if (!data.isReadable()) {
nextEntry = null;
}
else {
// read entry at current data position
nextEntry = readEntry(data, nextEntry);
}
return entry;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
/**
* Repositions the iterator so the beginning of this block.
*/
@Override
public void seekToFirst()
{
if (restartCount > 0) {
seekToRestartPosition(0);
}
}
/**
* Repositions the iterator so the key of the next BlockElement returned greater than or equal to the specified targetKey.
*/
@Override
public void seek(Slice targetKey)
{
if (restartCount == 0) {
return;
}
int left = 0;
int right = restartCount - 1;
// binary search restart positions to find the restart position immediately before the targetKey
while (left < right) {
int mid = (left + right + 1) / 2;
seekToRestartPosition(mid);
if (comparator.compare(nextEntry.getKey(), targetKey) < 0) {
// key at mid is smaller than targetKey. Therefore all restart
// blocks before mid are uninteresting.
left = mid;
}
else {
// key at mid is greater than or equal to targetKey. Therefore
// all restart blocks at or after mid are uninteresting.
right = mid - 1;
}
}
// linear search (within restart block) for first key greater than or equal to targetKey
for (seekToRestartPosition(left); nextEntry != null; next()) {
if (comparator.compare(peek().getKey(), targetKey) >= 0) {
break;
}
}
}
/**
* Seeks to and reads the entry at the specified restart position.
*
* After this method, nextEntry will contain the next entry to return, and the previousEntry will be null.
*/
private void seekToRestartPosition(int restartPosition)
{
Preconditions.checkPositionIndex(restartPosition, restartCount, "restartPosition");
// seek data readIndex to the beginning of the restart block
int offset = restartPositions.getInt(restartPosition * SIZE_OF_INT);
data.setPosition(offset);
// clear the entries to assure key is not prefixed
nextEntry = null;
// read the entry
nextEntry = readEntry(data, null);
}
/**
* Reads the entry at the current data readIndex.
* After this method, data readIndex is positioned at the beginning of the next entry
* or at the end of data if there was not a next entry.
*
* @return true if an entry was read
*/
private static BlockEntry readEntry(SliceInput data, BlockEntry previousEntry)
{
Preconditions.checkNotNull(data, "data is null");
// read entry header
int sharedKeyLength = VariableLengthQuantity.readVariableLengthInt(data);
int nonSharedKeyLength = VariableLengthQuantity.readVariableLengthInt(data);
int valueLength = VariableLengthQuantity.readVariableLengthInt(data);
// read key
Slice key = Slices.allocate(sharedKeyLength + nonSharedKeyLength);
SliceOutput sliceOutput = key.output();
if (sharedKeyLength > 0) {
Preconditions.checkState(previousEntry != null, "Entry has a shared key but no previous entry was provided");
sliceOutput.writeBytes(previousEntry.getKey(), 0, sharedKeyLength);
}
sliceOutput.writeBytes(data, nonSharedKeyLength);
// read value
Slice value = data.readSlice(valueLength);
return new BlockEntry(key, value);
}
}