com.palantir.atlasdb.keyvalue.dbkvs.impl.sweep.CandidateGroupingIterator Maven / Gradle / Ivy

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/*
 * (c) Copyright 2018 Palantir Technologies Inc. All rights reserved.
 *
 * 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 com.palantir.atlasdb.keyvalue.dbkvs.impl.sweep;

import com.palantir.atlasdb.encoding.PtBytes;
import com.palantir.atlasdb.keyvalue.api.CandidateCellForSweeping;
import com.palantir.atlasdb.keyvalue.api.Cell;
import com.palantir.atlasdb.keyvalue.api.ImmutableCandidateCellForSweeping;
import com.palantir.logsafe.Preconditions;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;
import org.eclipse.collections.api.list.primitive.MutableLongList;
import org.eclipse.collections.impl.factory.primitive.LongLists;

public final class CandidateGroupingIterator implements Iterator> {
    private final Iterator> cellTsIterator;

    private byte[] currentRowName = PtBytes.EMPTY_BYTE_ARRAY;
    private byte[] currentColName = PtBytes.EMPTY_BYTE_ARRAY;
    private final MutableLongList currentCellTimestamps = LongLists.mutable.empty();
    private boolean currentIsLatestValueEmpty = false;

    private CandidateGroupingIterator(Iterator> cellTsIterator) {
        this.cellTsIterator = cellTsIterator;
    }

    /** The 'cellTsIterator' is expected to return (cell, ts) pairs in strict lexicographically increasing order.
     **/
    public static Iterator> create(Iterator> cellTsIterator) {
        return new CandidateGroupingIterator(cellTsIterator);
    }

    @Override
    public boolean hasNext() {
        return cellTsIterator.hasNext();
    }

    @Override
    public List next() {
        Preconditions.checkState(hasNext());
        List cellTsBatch = cellTsIterator.next();
        List candidates = new ArrayList<>();
        for (CellTsPairInfo cellTs : cellTsBatch) {
            checkCurrentCellAndUpdateIfNecessary(cellTs).ifPresent(candidates::add);
            if (currentCellTimestamps.size() > 0) {
                // We expect the timestamps in ascending order. This check costs us a few CPU cycles
                // but it's worth it for paranoia reasons - mistaking a cell with data for an empty one
                // can cause data corruption.
                Preconditions.checkArgument(
                        cellTs.ts > currentCellTimestamps.get(currentCellTimestamps.size() - 1),
                        "Timestamps for each cell must be fed in strictly increasing order");
            }
            updateStateAfterSingleCellTsPairProcessed(cellTs);
        }
        if (!cellTsIterator.hasNext()) {
            getCurrentCandidate().ifPresent(candidates::add);
        }
        return candidates;
    }

    private void updateStateAfterSingleCellTsPairProcessed(CellTsPairInfo cellTs) {
        currentIsLatestValueEmpty = cellTs.hasEmptyValue;
        currentCellTimestamps.add(cellTs.ts);
    }

    private Optional checkCurrentCellAndUpdateIfNecessary(CellTsPairInfo cellTs) {
        if (isCurrentCell(cellTs)) {
            return Optional.empty();
        } else {
            Optional candidate = getCurrentCandidate();
            updateStateForNewCell(cellTs);
            return candidate;
        }
    }

    private boolean isCurrentCell(CellTsPairInfo cellTs) {
        return Arrays.equals(currentRowName, cellTs.rowName) && Arrays.equals(currentColName, cellTs.colName);
    }

    private Optional getCurrentCandidate() {
        if (currentCellTimestamps.isEmpty()) {
            return Optional.empty();
        } else {
            return Optional.of(ImmutableCandidateCellForSweeping.builder()
                    .cell(Cell.create(currentRowName, currentColName))
                    .sortedTimestamps(toList(currentCellTimestamps))
                    .isLatestValueEmpty(currentIsLatestValueEmpty)
                    .build());
        }
    }

    private Collection toList(MutableLongList values) {
        return values.collect(Long::valueOf, new ArrayList<>(values.size()));
    }

    private void updateStateForNewCell(CellTsPairInfo cell) {
        currentCellTimestamps.clear();
        currentRowName = cell.rowName;
        currentColName = cell.colName;
        currentIsLatestValueEmpty = false;
    }
}