src/java/org/apache/cassandra/db/commitlog/ReplayPosition.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.commitlog;

import java.io.IOException;
import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;

import com.google.common.collect.Ordering;

import org.apache.cassandra.db.TypeSizes;
import org.apache.cassandra.io.ISerializer;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.io.util.DataInputPlus;
import org.apache.cassandra.io.util.DataOutputPlus;

public class ReplayPosition implements Comparable<ReplayPosition>
{
    public static final ReplayPositionSerializer serializer = new ReplayPositionSerializer();

    // NONE is used for SSTables that are streamed from other nodes and thus have no relationship
    // with our local commitlog. The values satisfy the criteria that
    //  - no real commitlog segment will have the given id
    //  - it will sort before any real replayposition, so it will be effectively ignored by getReplayPosition
    public static final ReplayPosition NONE = new ReplayPosition(-1, 0);

    public final long segment;
    public final int position;

    /**
     * A filter of known safe-to-discard commit log replay positions, based on
     * the range covered by on disk sstables and those prior to the most recent truncation record
     */
    public static class ReplayFilter
    {
        final NavigableMap<ReplayPosition, ReplayPosition> persisted = new TreeMap<>();
        public ReplayFilter(Iterable<SSTableReader> onDisk, ReplayPosition truncatedAt)
        {
            for (SSTableReader reader : onDisk)
            {
                ReplayPosition start = reader.getSSTableMetadata().commitLogLowerBound;
                ReplayPosition end = reader.getSSTableMetadata().commitLogUpperBound;
                add(persisted, start, end);
            }
            if (truncatedAt != null)
                add(persisted, ReplayPosition.NONE, truncatedAt);
        }

        private static void add(NavigableMap<ReplayPosition, ReplayPosition> ranges, ReplayPosition start, ReplayPosition end)
        {
            // extend ourselves to cover any ranges we overlap
            // record directly preceding our end may extend past us, so take the max of our end and its
            Map.Entry<ReplayPosition, ReplayPosition> extend = ranges.floorEntry(end);
            if (extend != null && extend.getValue().compareTo(end) > 0)
                end = extend.getValue();

            // record directly preceding our start may extend into us; if it does, we take it as our start
            extend = ranges.lowerEntry(start);
            if (extend != null && extend.getValue().compareTo(start) >= 0)
                start = extend.getKey();

            ranges.subMap(start, end).clear();
            ranges.put(start, end);
        }

        public boolean shouldReplay(ReplayPosition position)
        {
            // replay ranges are start exclusive, end inclusive
            Map.Entry<ReplayPosition, ReplayPosition> range = persisted.lowerEntry(position);
            return range == null || position.compareTo(range.getValue()) > 0;
        }

        public boolean isEmpty()
        {
            return persisted.isEmpty();
        }
    }

    public static ReplayPosition firstNotCovered(Iterable<ReplayFilter> ranges)
    {
        ReplayPosition min = null;
        for (ReplayFilter map : ranges)
        {
            ReplayPosition first = map.persisted.firstEntry().getValue();
            if (min == null)
                min = first;
            else
                min = Ordering.natural().min(min, first);
        }
        if (min == null)
            return NONE;
        return min;
    }

    public ReplayPosition(long segment, int position)
    {
        this.segment = segment;
        assert position >= 0;
        this.position = position;
    }

    public int compareTo(ReplayPosition that)
    {
        if (this.segment != that.segment)
            return Long.compare(this.segment, that.segment);

        return Integer.compare(this.position, that.position);
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        ReplayPosition that = (ReplayPosition) o;

        if (position != that.position) return false;
        return segment == that.segment;
    }

    @Override
    public int hashCode()
    {
        int result = (int) (segment ^ (segment >>> 32));
        result = 31 * result + position;
        return result;
    }

    @Override
    public String toString()
    {
        return "ReplayPosition(" +
               "segmentId=" + segment +
               ", position=" + position +
               ')';
    }

    public ReplayPosition clone()
    {
        return new ReplayPosition(segment, position);
    }

    public static class ReplayPositionSerializer implements ISerializer<ReplayPosition>
    {
        public void serialize(ReplayPosition rp, DataOutputPlus out) throws IOException
        {
            out.writeLong(rp.segment);
            out.writeInt(rp.position);
        }

        public ReplayPosition deserialize(DataInputPlus in) throws IOException
        {
            return new ReplayPosition(in.readLong(), in.readInt());
        }

        public long serializedSize(ReplayPosition rp)
        {
            return TypeSizes.sizeof(rp.segment) + TypeSizes.sizeof(rp.position);
        }
    }
}