maedhroz commented on code in PR #2267: URL: https://github.com/apache/cassandra/pull/2267#discussion_r1183966836
########## src/java/org/apache/cassandra/io/sstable/format/bti/SSTableReversedIterator.java: ########## @@ -0,0 +1,295 @@ +/* + * 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.io.sstable.format.bti; + +import java.io.IOException; +import java.util.NoSuchElementException; + +import com.carrotsearch.hppc.LongStack; +import org.apache.cassandra.db.ClusteringBound; +import org.apache.cassandra.db.ClusteringComparator; +import org.apache.cassandra.db.DecoratedKey; +import org.apache.cassandra.db.Slice; +import org.apache.cassandra.db.Slices; +import org.apache.cassandra.db.UnfilteredValidation; +import org.apache.cassandra.db.filter.ColumnFilter; +import org.apache.cassandra.db.rows.RangeTombstoneBoundMarker; +import org.apache.cassandra.db.rows.RangeTombstoneMarker; +import org.apache.cassandra.db.rows.Unfiltered; +import org.apache.cassandra.io.sstable.AbstractRowIndexEntry; +import org.apache.cassandra.io.sstable.AbstractSSTableIterator; +import org.apache.cassandra.io.sstable.format.bti.RowIndexReader.IndexInfo; +import org.apache.cassandra.io.util.FileDataInput; +import org.apache.cassandra.io.util.FileHandle; + +/** + * Unfiltered row iterator over a BTI SSTable that returns rows in reverse order. + */ +class SSTableReversedIterator extends AbstractSSTableIterator<TrieIndexEntry> +{ + /** + * The index of the slice being processed. + */ + private int slice; + + public SSTableReversedIterator(BtiTableReader sstable, + FileDataInput file, + DecoratedKey key, + TrieIndexEntry indexEntry, + Slices slices, + ColumnFilter columns, + FileHandle ifile) + { + super(sstable, file, key, indexEntry, slices, columns, ifile); + } + + protected Reader createReaderInternal(TrieIndexEntry indexEntry, FileDataInput file, boolean shouldCloseFile) + { + if (indexEntry.isIndexed()) + return new ReverseIndexedReader(indexEntry, file, shouldCloseFile); + else + return 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(); + } + + /** + * Reverse iteration is performed by going through an index block (or the whole partition if not indexed) forwards + * and storing the positions of each entry that falls within the slice in a stack. Reverse iteration then pops out + * positions and reads the entries. + * <p> + * Note: The earlier version of this was constructing an in-memory view of the block instead, which gives better + * performance on bigger queries and index blocks (due to not having to read disk again). With the lower + * granularity of the tries it makes better sense to store as little as possible as the beginning of the block + * should very rarely be in other page/chunk cache locations. This has the benefit of being able to answer small + * queries (esp. LIMIT 1) faster and with less GC churn. + */ + private class ReverseReader extends AbstractReader + { + final LongStack rowOffsets = new LongStack(); + RangeTombstoneMarker blockOpenMarker, blockCloseMarker; + private Unfiltered next = null; + private boolean foundLessThan; + private long startPos = -1; + + private ReverseReader(FileDataInput file, boolean shouldCloseFile) + { + super(file, shouldCloseFile); + } + + @Override + public void setForSlice(Slice slice) throws IOException + { + // read full row and filter + if (startPos == -1) + startPos = file.getFilePointer(); + else + seekToPosition(startPos); + + fillOffsets(slice, true, true, Long.MAX_VALUE); + } + + @Override + protected boolean hasNextInternal() throws IOException + { + if (next != null) + return true; + next = computeNext(); + return next != null; + } + + @Override + protected Unfiltered nextInternal() throws IOException + { + if (!hasNextInternal()) + throw new NoSuchElementException(); + + Unfiltered toReturn = next; + next = null; + return toReturn; + } + + private Unfiltered computeNext() throws IOException + { + Unfiltered toReturn; + do + { + if (blockCloseMarker != null) + { + toReturn = blockCloseMarker; + blockCloseMarker = null; + return toReturn; + } + while (!rowOffsets.isEmpty()) + { + seekToPosition(rowOffsets.pop()); + boolean hasNext = deserializer.hasNext(); + assert hasNext; + toReturn = deserializer.readNext(); + UnfilteredValidation.maybeValidateUnfiltered(toReturn, metadata(), key, sstable); + // We may get empty row for the same reason expressed on UnfilteredSerializer.deserializeOne. + if (!toReturn.isEmpty()) + return toReturn; + } + } + while (!foundLessThan && advanceIndexBlock()); + + // open marker to be output only as slice is finished + if (blockOpenMarker != null) + { + toReturn = blockOpenMarker; + blockOpenMarker = null; + return toReturn; + } + return null; + } + + protected boolean advanceIndexBlock() throws IOException + { + return false; + } + + void fillOffsets(Slice slice, boolean filterStart, boolean filterEnd, long stopPosition) throws IOException + { + filterStart &= !slice.start().equals(ClusteringBound.BOTTOM); + filterEnd &= !slice.end().equals(ClusteringBound.TOP); + + ClusteringBound<?> start = slice.start(); + long currentPosition = file.getFilePointer(); + foundLessThan = false; + // This is a copy of handlePreSliceData which also checks currentPosition < stopPosition. + // Not extracted to method as we need both marker and currentPosition. + if (filterStart) + { + while (currentPosition < stopPosition && deserializer.hasNext() && deserializer.compareNextTo(start) <= 0) + { + if (deserializer.nextIsRow()) + deserializer.skipNext(); + else + updateOpenMarker((RangeTombstoneMarker) deserializer.readNext()); + + currentPosition = file.getFilePointer(); + foundLessThan = true; + } + } + + // We've reached the beginning of our queried slice. If we have an open marker + // we should return that at the end of the slice to close the deletion. + if (openMarker != null) + blockOpenMarker = new RangeTombstoneBoundMarker(start, openMarker); + + + // 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 (currentPosition < stopPosition && deserializer.hasNext() + && (!filterEnd || deserializer.compareNextTo(slice.end()) < 0)) + { + rowOffsets.push(currentPosition); + if (deserializer.nextIsRow()) + deserializer.skipNext(); + else + updateOpenMarker((RangeTombstoneMarker) deserializer.readNext()); + + currentPosition = file.getFilePointer(); + } + + // If we have an open marker, we should output that first, unless end is not being filtered + // (i.e. it's either top (where a marker can't be open) or we placed that marker during previous block). + if (openMarker != null && filterEnd) + { + // If we have no end and still an openMarker, this means we're indexed and the marker is closed in a following block. + blockCloseMarker = new RangeTombstoneBoundMarker(slice.end(), openMarker); + openMarker = null; + } + } + } + + private class ReverseIndexedReader extends ReverseReader + { + private RowIndexReverseIterator indexReader; + private final TrieIndexEntry indexEntry; + private final long basePosition; Review Comment: nit: Not a big deal, but I wonder if naming this something like `partitionStart` or `partitionStartPosition` would make it more readable. -- This is an automated message from the Apache Git Service. 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