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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.cassandra.db.columniterator;
import java.io.IOException;
import java.util.*;
import org.apache.cassandra.db.*;
import org.apache.cassandra.db.filter.ColumnFilter;
import org.apache.cassandra.db.partitions.ImmutableBTreePartition;
import org.apache.cassandra.db.rows.*;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.io.util.FileDataInput;
import org.apache.cassandra.io.util.FileHandle;
import org.apache.cassandra.schema.TableMetadata;
import org.apache.cassandra.utils.AbstractIterator;
import org.apache.cassandra.utils.btree.BTree;
/**
* A Cell Iterator in reversed clustering order over SSTable
*/
public class SSTableReversedIterator extends AbstractSSTableIterator
{
/**
* The index of the slice being processed.
*/
private int slice;
public SSTableReversedIterator(SSTableReader sstable,
FileDataInput file,
DecoratedKey key,
RowIndexEntry indexEntry,
Slices slices,
ColumnFilter columns,
FileHandle ifile)
{
super(sstable, file, key, indexEntry, slices, columns, ifile);
}
protected Reader createReaderInternal(RowIndexEntry indexEntry, FileDataInput file, boolean shouldCloseFile)
{
return indexEntry.isIndexed()
? new ReverseIndexedReader(indexEntry, file, shouldCloseFile)
: new ReverseReader(file, shouldCloseFile);
}
public boolean isReverseOrder()
{
return true;
}
protected int nextSliceIndex()
{
int next = slice;
slice++;
return slices.size() - (next + 1);
}
protected boolean hasMoreSlices()
{
return slice < slices.size();
}
private class ReverseReader extends Reader
{
protected ReusablePartitionData buffer;
protected Iterator iterator;
// Set in loadFromDisk () and used in setIterator to handle range tombstone extending on multiple index block. See
// loadFromDisk for details. Note that those are always false for non-indexed readers.
protected boolean skipFirstIteratedItem;
protected boolean skipLastIteratedItem;
private ReverseReader(FileDataInput file, boolean shouldCloseFile)
{
super(file, shouldCloseFile);
}
protected ReusablePartitionData createBuffer(int blocksCount)
{
int estimatedRowCount = 16;
int columnCount = metadata().regularColumns().size();
if (columnCount == 0 || metadata().clusteringColumns().isEmpty())
{
estimatedRowCount = 1;
}
else
{
try
{
// To avoid wasted resizing we guess-estimate the number of rows we're likely to read. For that
// we use the stats on the number of rows per partition for that sstable.
// FIXME: so far we only keep stats on cells, so to get a rough estimate on the number of rows,
// we divide by the number of regular columns the table has. We should fix once we collect the
// stats on rows
int estimatedRowsPerPartition = (int)(sstable.getEstimatedCellPerPartitionCount().percentile(0.75) / columnCount);
estimatedRowCount = Math.max(estimatedRowsPerPartition / blocksCount, 1);
}
catch (IllegalStateException e)
{
// The EstimatedHistogram mean() method can throw this (if it overflows). While such overflow
// shouldn't happen, it's not worth taking the risk of letting the exception bubble up.
}
}
return new ReusablePartitionData(metadata(), partitionKey(), columns(), estimatedRowCount);
}
public void setForSlice(Slice slice) throws IOException
{
// If we have read the data, just create the iterator for the slice. Otherwise, read the data.
if (buffer == null)
{
buffer = createBuffer(1);
// Note that we can reuse that buffer between slices (we could alternatively re-read from disk
// every time, but that feels more wasteful) so we want to include everything from the beginning.
// We can stop at the slice end however since any following slice will be before that.
loadFromDisk(null, slice.end(), false, false);
}
setIterator(slice);
}
protected void setIterator(Slice slice)
{
assert buffer != null;
iterator = buffer.built.unfilteredIterator(columns, Slices.with(metadata().comparator, slice), true);
if (!iterator.hasNext())
return;
if (skipFirstIteratedItem)
iterator.next();
if (skipLastIteratedItem)
iterator = new SkipLastIterator(iterator);
}
protected boolean hasNextInternal() throws IOException
{
// If we've never called setForSlice, we're reading everything
if (iterator == null)
setForSlice(Slice.ALL);
return iterator.hasNext();
}
protected Unfiltered nextInternal() throws IOException
{
if (!hasNext())
throw new NoSuchElementException();
return iterator.next();
}
protected boolean stopReadingDisk() throws IOException
{
return false;
}
// Reads the unfiltered from disk and load them into the reader buffer. It stops reading when either the partition
// is fully read, or when stopReadingDisk() returns true.
protected void loadFromDisk(ClusteringBound start,
ClusteringBound end,
boolean hasPreviousBlock,
boolean hasNextBlock) throws IOException
{
// start != null means it's the block covering the beginning of the slice, so it has to be the last block for this slice.
assert start == null || !hasNextBlock;
buffer.reset();
skipFirstIteratedItem = false;
skipLastIteratedItem = false;
// If the start might be in this block, skip everything that comes before it.
if (start != null)
{
while (deserializer.hasNext() && deserializer.compareNextTo(start) <= 0 && !stopReadingDisk())
{
if (deserializer.nextIsRow())
deserializer.skipNext();
else
updateOpenMarker((RangeTombstoneMarker)deserializer.readNext());
}
}
// If we have an open marker, it's either one from what we just skipped or it's one that open in the next (or
// one of the next) index block (if openMarker == openMarkerAtStartOfBlock).
if (openMarker != null)
{
// We have to feed a marker to the buffer, because that marker is likely to be close later and ImmtableBTreePartition
// doesn't take kindly to marker that comes without their counterpart. If that's the last block we're gonna read (for
// the current slice at least) it's easy because we'll want to return that open marker at the end of the data in this
// block anyway, so we have nothing more to do than adding it to the buffer.
// If it's not the last block however, in which case we know we'll have start == null, it means this marker is really
// open in a next block and so while we do need to add it the buffer for the reason mentioned above, we don't
// want to "return" it just yet, we'll wait until we reach it in the next blocks. That's why we trigger
// skipLastIteratedItem in that case (this is first item of the block, but we're iterating in reverse order
// so it will be last returned by the iterator).
ClusteringBound markerStart = start == null ? BufferClusteringBound.BOTTOM : start;
buffer.add(new RangeTombstoneBoundMarker(markerStart, openMarker));
if (hasNextBlock)
skipLastIteratedItem = true;
}
// Now deserialize everything until we reach our requested end (if we have one)
// See SSTableIterator.ForwardRead.computeNext() for why this is a strict inequality below: this is the same
// reasoning here.
while (deserializer.hasNext()
&& (end == null || deserializer.compareNextTo(end) < 0)
&& !stopReadingDisk())
{
Unfiltered unfiltered = deserializer.readNext();
UnfilteredValidation.maybeValidateUnfiltered(unfiltered, metadata(), key, sstable);
// We may get empty row for the same reason expressed on UnfilteredSerializer.deserializeOne.
if (!unfiltered.isEmpty())
buffer.add(unfiltered);
if (unfiltered.isRangeTombstoneMarker())
updateOpenMarker((RangeTombstoneMarker)unfiltered);
}
// If we have an open marker, we should close it before finishing
if (openMarker != null)
{
// This is the reverse problem than the one at the start of the block. Namely, if it's the first block
// we deserialize for the slice (the one covering the slice end basically), then it's easy, we just want
// to add the close marker to the buffer and return it normally.
// If it's note our first block (for the slice) however, it means that marker closed in a previously read
// block and we have already returned it. So while we should still add it to the buffer for the sake of
// not breaking ImmutableBTreePartition, we should skip it when returning from the iterator, hence the
// skipFirstIteratedItem (this is the last item of the block, but we're iterating in reverse order so it will
// be the first returned by the iterator).
ClusteringBound markerEnd = end == null ? BufferClusteringBound.TOP : end;
buffer.add(new RangeTombstoneBoundMarker(markerEnd, openMarker));
if (hasPreviousBlock)
skipFirstIteratedItem = true;
}
buffer.build();
}
}
private class ReverseIndexedReader extends ReverseReader
{
private final IndexState indexState;
// The slice we're currently iterating over
private Slice slice;
// The last index block to consider for the slice
private int lastBlockIdx;
private ReverseIndexedReader(RowIndexEntry indexEntry, FileDataInput file, boolean shouldCloseFile)
{
super(file, shouldCloseFile);
this.indexState = new IndexState(this, metadata.comparator, indexEntry, true, ifile);
}
@Override
public void close() throws IOException
{
super.close();
this.indexState.close();
}
@Override
public void setForSlice(Slice slice) throws IOException
{
this.slice = slice;
// if our previous slicing already got us past the beginning of the sstable, we're done
if (indexState.isDone())
{
iterator = Collections.emptyIterator();
return;
}
// Find the first index block we'll need to read for the slice.
int startIdx = indexState.findBlockIndex(slice.end(), indexState.currentBlockIdx());
if (startIdx < 0)
{
iterator = Collections.emptyIterator();
indexState.setToBlock(startIdx);
return;
}
lastBlockIdx = indexState.findBlockIndex(slice.start(), startIdx);
// If the last block to look (in reverse order) is after the very last block, we have nothing for that slice
if (lastBlockIdx >= indexState.blocksCount())
{
assert startIdx >= indexState.blocksCount();
iterator = Collections.emptyIterator();
return;
}
// If we start (in reverse order) after the very last block, just read from the last one.
if (startIdx >= indexState.blocksCount())
startIdx = indexState.blocksCount() - 1;
// Note that even if we were already set on the proper block (which would happen if the previous slice
// requested ended on the same block this one start), we can't reuse it because when reading the previous
// slice we've only read that block from the previous slice start. Re-reading also handles
// skipFirstIteratedItem/skipLastIteratedItem that we would need to handle otherwise.
indexState.setToBlock(startIdx);
readCurrentBlock(false, startIdx != lastBlockIdx);
}
@Override
protected boolean hasNextInternal() throws IOException
{
if (super.hasNextInternal())
return true;
while (true)
{
// We have nothing more for our current block, move the next one (so the one before on disk).
int nextBlockIdx = indexState.currentBlockIdx() - 1;
if (nextBlockIdx < 0 || nextBlockIdx < lastBlockIdx)
return false;
// The slice start can be in
indexState.setToBlock(nextBlockIdx);
readCurrentBlock(true, nextBlockIdx != lastBlockIdx);
// If an indexed block only contains data for a dropped column, the iterator will be empty, even
// though we may still have data to read in subsequent blocks
// also, for pre-3.0 storage formats, index blocks that only contain a single row and that row crosses
// index boundaries, the iterator will be empty even though we haven't read everything we're intending
// to read. In that case, we want to read the next index block. This shouldn't be possible in 3.0+
// formats (see next comment)
if (!iterator.hasNext() && nextBlockIdx > lastBlockIdx)
{
continue;
}
return iterator.hasNext();
}
}
/**
* Reads the current block, the last one we've set.
*
* @param hasPreviousBlock is whether we have already read a previous block for the current slice.
* @param hasNextBlock is whether we have more blocks to read for the current slice.
*/
private void readCurrentBlock(boolean hasPreviousBlock, boolean hasNextBlock) throws IOException
{
if (buffer == null)
buffer = createBuffer(indexState.blocksCount());
// The slice start (resp. slice end) is only meaningful on the last (resp. first) block read (since again,
// we read blocks in reverse order).
boolean canIncludeSliceStart = !hasNextBlock;
boolean canIncludeSliceEnd = !hasPreviousBlock;
loadFromDisk(canIncludeSliceStart ? slice.start() : null,
canIncludeSliceEnd ? slice.end() : null,
hasPreviousBlock,
hasNextBlock);
setIterator(slice);
}
@Override
protected boolean stopReadingDisk() throws IOException
{
return indexState.isPastCurrentBlock();
}
}
private class ReusablePartitionData
{
private final TableMetadata metadata;
private final DecoratedKey partitionKey;
private final RegularAndStaticColumns columns;
private MutableDeletionInfo.Builder deletionBuilder;
private MutableDeletionInfo deletionInfo;
private BTree.Builder rowBuilder;
private ImmutableBTreePartition built;
private ReusablePartitionData(TableMetadata metadata,
DecoratedKey partitionKey,
RegularAndStaticColumns columns,
int initialRowCapacity)
{
this.metadata = metadata;
this.partitionKey = partitionKey;
this.columns = columns;
this.rowBuilder = BTree.builder(metadata.comparator, initialRowCapacity);
}
public void add(Unfiltered unfiltered)
{
if (unfiltered.isRow())
rowBuilder.add((Row)unfiltered);
else
deletionBuilder.add((RangeTombstoneMarker)unfiltered);
}
public void reset()
{
built = null;
rowBuilder.reuse();
deletionBuilder = MutableDeletionInfo.builder(partitionLevelDeletion, metadata().comparator, false);
}
public void build()
{
deletionInfo = deletionBuilder.build();
built = new ImmutableBTreePartition(metadata, partitionKey, columns, Rows.EMPTY_STATIC_ROW, rowBuilder.build(),
deletionInfo, EncodingStats.NO_STATS);
deletionBuilder = null;
}
}
private static class SkipLastIterator extends AbstractIterator
{
private final Iterator iterator;
private SkipLastIterator(Iterator iterator)
{
this.iterator = iterator;
}
protected Unfiltered computeNext()
{
if (!iterator.hasNext())
return endOfData();
Unfiltered next = iterator.next();
return iterator.hasNext() ? next : endOfData();
}
}
}