cassandra-trunk/src/java/org/apache/cassandra/db/rows/UnfilteredRowIterators.java
/*
 * 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.rows;

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.cassandra.db.Columns;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.DeletionTime;
import org.apache.cassandra.db.Digest;
import org.apache.cassandra.db.EmptyIterators;
import org.apache.cassandra.db.RegularAndStaticColumns;
import org.apache.cassandra.db.filter.ColumnFilter;
import org.apache.cassandra.db.transform.FilteredRows;
import org.apache.cassandra.db.transform.MoreRows;
import org.apache.cassandra.db.transform.Transformation;
import org.apache.cassandra.io.sstable.CorruptSSTableException;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.schema.TableMetadata;
import org.apache.cassandra.serializers.MarshalException;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.IMergeIterator;
import org.apache.cassandra.utils.MergeIterator;

/**
 * Static methods to work with atom iterators.
 */
public abstract class UnfilteredRowIterators
{
    private static final Logger logger = LoggerFactory.getLogger(UnfilteredRowIterators.class);

    private UnfilteredRowIterators() {}

    /**
     * Interface for a listener interested in the result of merging multiple versions of a given row.
     * <p>
     * Implementors of this interface are given enough information that they can easily reconstruct the difference
     * between the merged result and each individual input. This is used when reconciling results on replias for
     * instance to figure out what to send as read-repair to each source.
     */
    public interface MergeListener
    {
        /**
         * Called once for the merged partition.
         *
         * @param mergedDeletion the partition level deletion for the merged partition. Implementors can test if the
         * merged partition actually has a partition level deletion or not by calling {@code mergedDeletion.isLive()}.
         * @param versions the partition level deletion for the sources of the merge. Elements of the array will never
         * be null, but be "live".
         **/
        public void onMergedPartitionLevelDeletion(DeletionTime mergedDeletion, DeletionTime[] versions);

        /**
         * Called once for every row participating in the merge.
         * <p>
         * Note that this is called for every clustering where at least one of the source merged has a row. In
         * particular, this may be called in cases where there is no row in the merged output (if a source has a row
         * that is shadowed by another source range tombstone or partition level deletion).
         *
         * @param merged the result of the merge. This cannot be {@code null} (so that listener can always access the
         * clustering from this safely)but can be empty, in which case this is a placeholder for when at least one
         * source has a row, but that row is shadowed in the merged output.
         * @param versions for each source, the row in that source corresponding to {@code merged}. This can be
         * {@code null} for some sources if the source has not such row.
         * @return the row to use as result of the merge (can be {@code null}). Most implementations should simply
         * return {@code merged}, but this allows some implementations to impact the merge result if necessary. If this
         * returns either {@code null} or an empty row, then the row is skipped from the merge result. If this returns a
         * non {@code null} result, then the returned row <b>must</b> have the same clustering than {@code merged}.
         */
        public Row onMergedRows(Row merged, Row[] versions);

        /**
         * Called once for every range tombstone marker participating in the merge.
         * <p>
         * Note that this is called for every "clustering position" where at least one of the source merged has a range
         * tombstone marker.
         *
         * @param merged the marker in the merged output. This can be {@code null} if there is no such marker, which
         * means that at least one source has a marker in {@code versions} but the merged out has nothing corresponding
         * (this basically mean the merged output has a currently open deletion that shadows whatever marker the source
         * had).
         * @param versions the marker for each source merged. This can be {@code null} for some source if that source
         * has not such marker.
         */
        public void onMergedRangeTombstoneMarkers(RangeTombstoneMarker merged, RangeTombstoneMarker[] versions);

        public void close();

        public static MergeListener NOOP = new MergeListener()
        {
            public void onMergedPartitionLevelDeletion(DeletionTime mergedDeletion, DeletionTime[] versions) {}

            public Row onMergedRows(Row merged, Row[] versions) {return merged;}

            public void onMergedRangeTombstoneMarkers(RangeTombstoneMarker merged, RangeTombstoneMarker[] versions) {}

            public void close() {}
        };
    }

    /**
     * Returns a iterator that only returns rows with only live content.
     *
     * This is mainly used in the CQL layer when we know we don't care about deletion
     * infos (and since an UnfilteredRowIterator cannot shadow it's own data, we know everyting
     * returned isn't shadowed by a tombstone).
     */
    public static RowIterator filter(UnfilteredRowIterator iter, long nowInSec)
    {
        return FilteredRows.filter(iter, nowInSec);
    }

    /**
     * Returns an iterator that is the result of merging other iterators.
     */
    public static UnfilteredRowIterator merge(List<UnfilteredRowIterator> iterators)
    {
        assert !iterators.isEmpty();
        if (iterators.size() == 1)
            return iterators.get(0);

        return UnfilteredRowMergeIterator.create(iterators, null);
    }

    /**
     * Returns an iterator that is the result of merging other iterators, and (optionally) using
     * specific MergeListener.
     *
     * Note that this method assumes that there is at least 2 iterators to merge.
     */
    public static UnfilteredRowIterator merge(List<UnfilteredRowIterator> iterators, MergeListener mergeListener)
    {
        return UnfilteredRowMergeIterator.create(iterators, mergeListener);
    }

    /**
     * Returns an empty unfiltered iterator for a given partition.
     */
    public static UnfilteredRowIterator noRowsIterator(final TableMetadata metadata, final DecoratedKey partitionKey, final Row staticRow, final DeletionTime partitionDeletion, final boolean isReverseOrder)
    {
        return EmptyIterators.unfilteredRow(metadata, partitionKey, isReverseOrder, staticRow, partitionDeletion);
    }

    public static UnfilteredRowIterator singleton(Unfiltered unfiltered,
                                                  TableMetadata metadata,
                                                  DecoratedKey partitionKey,
                                                  DeletionTime partitionLevelDeletion,
                                                  RegularAndStaticColumns columns,
                                                  Row staticRow,
                                                  boolean isReverseOrder,
                                                  EncodingStats encodingStats)
    {
        return new AbstractUnfilteredRowIterator(metadata, partitionKey, partitionLevelDeletion, columns, staticRow, isReverseOrder, encodingStats)
        {
            boolean isDone = false;

            protected Unfiltered computeNext()
            {
                if (!isDone)
                {
                    isDone = true;
                    return unfiltered;
                }

                return endOfData();
            }
        };
    }

    /**
     * Digests the partition represented by the provided iterator.
     *
     * @param iterator the iterator to digest.
     * @param digest the {@link Digest} to use.
     * @param version the messaging protocol to use when producing the digest.
     */
    public static void digest(UnfilteredRowIterator iterator, Digest digest, int version)
    {
        digest.update(iterator.partitionKey().getKey());
        iterator.partitionLevelDeletion().digest(digest);
        iterator.columns().regulars.digest(digest);
        // When serializing an iterator, we skip the static columns if the iterator has not static row, even if the
        // columns() object itself has some (the columns() is a superset of what the iterator actually contains, and
        // will correspond to the queried columns pre-serialization). So we must avoid taking the satic column names
        // into account if there is no static row or we'd have a digest mismatch between depending on whether the digest
        // is computed on an iterator that has been serialized or not (see CASSANDRA-12090)
        // TODO: in practice we could completely skip digesting the columns since they are more informative of what the
        // iterator may contain, and digesting the actual content is enough. And in fact, that would be more correct
        // (since again, the columns could be different without the information represented by the iterator being
        // different), but removing them entirely is stricly speaking a breaking change (it would create mismatches on
        // upgrade) so we can only do on the next protocol version bump.
        if (iterator.staticRow() != Rows.EMPTY_STATIC_ROW)
            iterator.columns().statics.digest(digest);
        digest.updateWithBoolean(iterator.isReverseOrder());
        iterator.staticRow().digest(digest);

        while (iterator.hasNext())
        {
            Unfiltered unfiltered = iterator.next();
            unfiltered.digest(digest);
        }
    }

    /**
     * Filter the provided iterator to exclude cells that have been fetched but are not queried by the user
     * (see ColumnFilter for detailes).
     *
     * @param iterator the iterator to filter.
     * @param filter the {@code ColumnFilter} to use when deciding which columns are the one queried by the
     * user. This should be the filter that was used when querying {@code iterator}.
     * @return the filtered iterator..
     */
    public static UnfilteredRowIterator withOnlyQueriedData(UnfilteredRowIterator iterator, ColumnFilter filter)
    {
        if (filter.allFetchedColumnsAreQueried())
            return iterator;

        return Transformation.apply(iterator, new WithOnlyQueriedData(filter));
    }

    /**
     * Returns an iterator that concatenate two atom iterators.
     * This method assumes that both iterator are from the same partition and that the atom from
     * {@code iter2} come after the ones of {@code iter1} (that is, that concatenating the iterator
     * make sense).
     */
    public static UnfilteredRowIterator concat(final UnfilteredRowIterator iter1, final UnfilteredRowIterator iter2)
    {
        assert iter1.metadata().id.equals(iter2.metadata().id)
            && iter1.partitionKey().equals(iter2.partitionKey())
            && iter1.partitionLevelDeletion().equals(iter2.partitionLevelDeletion())
            && iter1.isReverseOrder() == iter2.isReverseOrder()
            && iter1.staticRow().equals(iter2.staticRow());

        class Extend implements MoreRows<UnfilteredRowIterator>
        {
            boolean returned = false;
            public UnfilteredRowIterator moreContents()
            {
                if (returned)
                    return null;
                returned = true;
                return iter2;
            }
        }

        return MoreRows.extend(iter1, new Extend(), iter1.columns().mergeTo(iter2.columns()));
    }

    /**
     * Returns an iterator that concatenate the specified atom with the iterator.
     */
    public static UnfilteredRowIterator concat(final Unfiltered first, final UnfilteredRowIterator wrapped)
    {
        return new WrappingUnfilteredRowIterator()
        {
            private boolean hasReturnedFirst;

            @Override
            public UnfilteredRowIterator wrapped()
            {
                return wrapped;
            }

            @Override
            public boolean hasNext()
            {
                return hasReturnedFirst ? wrapped.hasNext() : true;
            }

            @Override
            public Unfiltered next()
            {
                if (!hasReturnedFirst)
                {
                    hasReturnedFirst = true;
                    return first;
                }
                return wrapped.next();
            }
        };
    }

    /**
     * Validate that the data of the provided iterator is valid, that is that the values
     * it contains are valid for the type they represent, and more generally that the
     * infos stored are sensible.
     *
     * This is mainly used by scrubber to detect problems in sstables.
     *
     * @param iterator the partition to check.
     * @param filename the name of the file the data is comming from.
     * @return an iterator that returns the same data than {@code iterator} but that
     * checks said data and throws a {@code CorruptedSSTableException} if it detects
     * invalid data.
     */
    public static UnfilteredRowIterator withValidation(UnfilteredRowIterator iterator, final String filename)
    {
        class Validator extends Transformation
        {
            @Override
            public Row applyToStatic(Row row)
            {
                validate(row);
                return row;
            }

            @Override
            public Row applyToRow(Row row)
            {
                validate(row);
                return row;
            }

            @Override
            public RangeTombstoneMarker applyToMarker(RangeTombstoneMarker marker)
            {
                validate(marker);
                return marker;
            }

            private void validate(Unfiltered unfiltered)
            {
                try
                {
                    unfiltered.validateData(iterator.metadata());
                }
                catch (MarshalException me)
                {
                    throw new CorruptSSTableException(me, filename);
                }
            }
        }
        return Transformation.apply(iterator, new Validator());
    }

    /**
     * Wraps the provided iterator so it logs the returned atoms for debugging purposes.
     * <p>
     * Note that this is only meant for debugging as this can log a very large amount of
     * logging at INFO.
     */
    public static UnfilteredRowIterator loggingIterator(UnfilteredRowIterator iterator, final String id, final boolean fullDetails)
    {
        TableMetadata metadata = iterator.metadata();
        logger.info("[{}] Logging iterator on {}.{}, partition key={}, reversed={}, deletion={}",
                    id,
                    metadata.keyspace,
                    metadata.name,
                    metadata.partitionKeyType.getString(iterator.partitionKey().getKey()),
                    iterator.isReverseOrder(),
                    iterator.partitionLevelDeletion().markedForDeleteAt());

        class Logger extends Transformation
        {
            @Override
            public Row applyToStatic(Row row)
            {
                if (!row.isEmpty())
                    logger.info("[{}] {}", id, row.toString(metadata, fullDetails));
                return row;
            }

            @Override
            public Row applyToRow(Row row)
            {
                logger.info("[{}] {}", id, row.toString(metadata, fullDetails));
                return row;
            }

            @Override
            public RangeTombstoneMarker applyToMarker(RangeTombstoneMarker marker)
            {
                logger.info("[{}] {}", id, marker.toString(metadata));
                return marker;
            }
        }
        return Transformation.apply(iterator, new Logger());
    }

    /**
     * A wrapper over MergeIterator to implement the UnfilteredRowIterator interface.
     */
    private static class UnfilteredRowMergeIterator extends AbstractUnfilteredRowIterator
    {
        private final IMergeIterator<Unfiltered, Unfiltered> mergeIterator;
        private final MergeListener listener;

        private UnfilteredRowMergeIterator(TableMetadata metadata,
                                           List<UnfilteredRowIterator> iterators,
                                           RegularAndStaticColumns columns,
                                           DeletionTime partitionDeletion,
                                           boolean reversed,
                                           MergeListener listener)
        {
            super(metadata,
                  iterators.get(0).partitionKey(),
                  partitionDeletion,
                  columns,
                  mergeStaticRows(iterators, columns.statics, listener, partitionDeletion),
                  reversed,
                  EncodingStats.merge(iterators, UnfilteredRowIterator::stats));

            this.mergeIterator = MergeIterator.get(iterators,
                                                   reversed ? metadata.comparator.reversed() : metadata.comparator,
                                                   new MergeReducer(iterators.size(), reversed, listener));
            this.listener = listener;
        }

        private static UnfilteredRowMergeIterator create(List<UnfilteredRowIterator> iterators, MergeListener listener)
        {
            try
            {
                checkForInvalidInput(iterators);
                return new UnfilteredRowMergeIterator(iterators.get(0).metadata(),
                                                      iterators,
                                                      collectColumns(iterators),
                                                      collectPartitionLevelDeletion(iterators, listener),
                                                      iterators.get(0).isReverseOrder(),
                                                      listener);
            }
            catch (RuntimeException | Error e)
            {
                try
                {
                    FBUtilities.closeAll(iterators);
                }
                catch (Exception suppressed)
                {
                    e.addSuppressed(suppressed);
                }
                throw e;
            }
        }

        @SuppressWarnings("resource") // We're not really creating any resource here
        private static void checkForInvalidInput(List<UnfilteredRowIterator> iterators)
        {
            if (iterators.isEmpty())
                return;

            UnfilteredRowIterator first = iterators.get(0);
            for (int i = 1; i < iterators.size(); i++)
            {
                UnfilteredRowIterator iter = iterators.get(i);
                assert first.metadata().id.equals(iter.metadata().id);
                assert first.partitionKey().equals(iter.partitionKey());
                assert first.isReverseOrder() == iter.isReverseOrder();
            }
        }

        @SuppressWarnings("resource") // We're not really creating any resource here
        private static DeletionTime collectPartitionLevelDeletion(List<UnfilteredRowIterator> iterators, MergeListener listener)
        {
            DeletionTime[] versions = listener == null ? null : new DeletionTime[iterators.size()];

            DeletionTime delTime = DeletionTime.LIVE;
            for (int i = 0; i < iterators.size(); i++)
            {
                UnfilteredRowIterator iter = iterators.get(i);
                DeletionTime iterDeletion = iter.partitionLevelDeletion();
                if (listener != null)
                    versions[i] = iterDeletion;
                if (!delTime.supersedes(iterDeletion))
                    delTime = iterDeletion;
            }
            if (listener != null)
                listener.onMergedPartitionLevelDeletion(delTime, versions);
            return delTime;
        }

        private static Row mergeStaticRows(List<UnfilteredRowIterator> iterators,
                                           Columns columns,
                                           MergeListener listener,
                                           DeletionTime partitionDeletion)
        {
            if (columns.isEmpty())
                return Rows.EMPTY_STATIC_ROW;

            if (iterators.stream().allMatch(iter -> iter.staticRow().isEmpty()))
                return Rows.EMPTY_STATIC_ROW;

            Row.Merger merger = new Row.Merger(iterators.size(), columns.hasComplex());
            for (int i = 0; i < iterators.size(); i++)
                merger.add(i, iterators.get(i).staticRow());

            Row merged = merger.merge(partitionDeletion);
            if (merged == null)
                merged = Rows.EMPTY_STATIC_ROW;
            if (listener == null)
                return merged;

            merged = listener.onMergedRows(merged, merger.mergedRows());
            // Note that onMergedRows can have returned null even though his input wasn't null
            return merged == null ? Rows.EMPTY_STATIC_ROW : merged;
        }

        private static RegularAndStaticColumns collectColumns(List<UnfilteredRowIterator> iterators)
        {
            RegularAndStaticColumns first = iterators.get(0).columns();
            Columns statics = first.statics;
            Columns regulars = first.regulars;
            for (int i = 1; i < iterators.size(); i++)
            {
                RegularAndStaticColumns cols = iterators.get(i).columns();
                statics = statics.mergeTo(cols.statics);
                regulars = regulars.mergeTo(cols.regulars);
            }
            return statics == first.statics && regulars == first.regulars
                 ? first
                 : new RegularAndStaticColumns(statics, regulars);
        }

        protected Unfiltered computeNext()
        {
            while (mergeIterator.hasNext())
            {
                Unfiltered merged = mergeIterator.next();
                if (merged != null)
                    return merged;
            }
            return endOfData();
        }

        public void close()
        {
            // This will close the input iterators
            FileUtils.closeQuietly(mergeIterator);

            if (listener != null)
                listener.close();
        }

        private class MergeReducer extends MergeIterator.Reducer<Unfiltered, Unfiltered>
        {
            private final MergeListener listener;

            private Unfiltered.Kind nextKind;

            private final Row.Merger rowMerger;
            private final RangeTombstoneMarker.Merger markerMerger;

            private MergeReducer(int size, boolean reversed, MergeListener listener)
            {
                this.rowMerger = new Row.Merger(size, columns().regulars.hasComplex());
                this.markerMerger = new RangeTombstoneMarker.Merger(size, partitionLevelDeletion(), reversed);
                this.listener = listener;
            }

            @Override
            public boolean trivialReduceIsTrivial()
            {
                // If we have a listener, we must signal it even when we have a single version
                return listener == null;
            }

            public void reduce(int idx, Unfiltered current)
            {
                nextKind = current.kind();
                if (nextKind == Unfiltered.Kind.ROW)
                    rowMerger.add(idx, (Row)current);
                else
                    markerMerger.add(idx, (RangeTombstoneMarker)current);
            }

            protected Unfiltered getReduced()
            {
                if (nextKind == Unfiltered.Kind.ROW)
                {
                    Row merged = rowMerger.merge(markerMerger.activeDeletion());
                    if (listener == null)
                        return merged;

                    merged = listener.onMergedRows(merged == null
                                                   ? BTreeRow.emptyRow(rowMerger.mergedClustering())
                                                   : merged,
                                                   rowMerger.mergedRows());

                    return merged == null || merged.isEmpty() ? null : merged;
                }
                else
                {
                    RangeTombstoneMarker merged = markerMerger.merge();
                    if (listener != null)
                        listener.onMergedRangeTombstoneMarkers(merged, markerMerger.mergedMarkers());
                    return merged;
                }
            }

            protected void onKeyChange()
            {
                if (nextKind == Unfiltered.Kind.ROW)
                    rowMerger.clear();
                else
                    markerMerger.clear();
            }
        }
    }

}