/*
 * 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.metrics;

import java.util.*;
import java.util.concurrent.ThreadPoolExecutor;

import com.codahale.metrics.Counter;
import com.codahale.metrics.Gauge;
import com.codahale.metrics.Meter;

import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.config.Schema;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.db.compaction.CompactionInfo;
import org.apache.cassandra.db.compaction.CompactionManager;

import static org.apache.cassandra.metrics.CassandraMetricsRegistry.Metrics;

/**
 * Metrics for compaction.
 */
public class CompactionMetrics implements CompactionManager.CompactionExecutorStatsCollector
{
    public static final MetricNameFactory factory = new DefaultNameFactory("Compaction");

    // a synchronized identity set of running tasks to their compaction info
    private static final Set<CompactionInfo.Holder> compactions = Collections.synchronizedSet(Collections.newSetFromMap(new IdentityHashMap<CompactionInfo.Holder, Boolean>()));

    /** Estimated number of compactions remaining to perform */
    public final Gauge<Integer> pendingTasks;
    /** Estimated number of compactions remaining to perform, group by keyspace and then table name */
    public final Gauge<Map<String, Map<String, Integer>>> pendingTasksByTableName;

    /** Number of completed compactions since server [re]start */
    public final Gauge<Long> completedTasks;
    /** Total number of compactions since server [re]start */
    public final Meter totalCompactionsCompleted;
    /** Total number of bytes compacted since server [re]start */
    public final Counter bytesCompacted;

    public CompactionMetrics(final ThreadPoolExecutor... collectors)
    {
        pendingTasks = Metrics.register(factory.createMetricName("PendingTasks"), new Gauge<Integer>()
        {
            public Integer getValue()
            {
                int n = 0;
                // add estimate number of compactions need to be done
                for (String keyspaceName : Schema.instance.getKeyspaces())
                {
                    for (ColumnFamilyStore cfs : Keyspace.open(keyspaceName).getColumnFamilyStores())
                        n += cfs.getCompactionStrategyManager().getEstimatedRemainingTasks();
                }
                // add number of currently running compactions
                return n + compactions.size();
            }
        });

        pendingTasksByTableName = Metrics.register(factory.createMetricName("PendingTasksByTableName"),
            new Gauge<Map<String, Map<String, Integer>>>()
        {
            @Override
            public Map<String, Map<String, Integer>> getValue() {
                Map<String, Map<String, Integer>> resultMap = new HashMap<>();
                // estimation of compactions need to be done
                for (String keyspaceName : Schema.instance.getKeyspaces())
                {
                    for (ColumnFamilyStore cfs : Keyspace.open(keyspaceName).getColumnFamilyStores())
                    {
                        int taskNumber = cfs.getCompactionStrategyManager().getEstimatedRemainingTasks();
                        if (taskNumber > 0)
                        {
                            if (!resultMap.containsKey(keyspaceName))
                            {
                                resultMap.put(keyspaceName, new HashMap<>());
                            }
                            resultMap.get(keyspaceName).put(cfs.getTableName(), taskNumber);
                        }
                    }
                }

                // currently running compactions
                for (CompactionInfo.Holder compaction : compactions)
                {
                    CFMetaData metaData = compaction.getCompactionInfo().getCFMetaData();
                    if (!resultMap.containsKey(metaData.ksName))
                    {
                        resultMap.put(metaData.ksName, new HashMap<>());
                    }

                    Map<String, Integer> tableNameToCountMap = resultMap.get(metaData.ksName);
                    if (tableNameToCountMap.containsKey(metaData.cfName))
                    {
                        tableNameToCountMap.put(metaData.cfName,
                                                tableNameToCountMap.get(metaData.cfName) + 1);
                    }
                    else
                    {
                        tableNameToCountMap.put(metaData.cfName, 1);
                    }
                }
                return resultMap;
            }
        });

        completedTasks = Metrics.register(factory.createMetricName("CompletedTasks"), new Gauge<Long>()
        {
            public Long getValue()
            {
                long completedTasks = 0;
                for (ThreadPoolExecutor collector : collectors)
                    completedTasks += collector.getCompletedTaskCount();
                return completedTasks;
            }
        });
        totalCompactionsCompleted = Metrics.meter(factory.createMetricName("TotalCompactionsCompleted"));
        bytesCompacted = Metrics.counter(factory.createMetricName("BytesCompacted"));
    }

    public void beginCompaction(CompactionInfo.Holder ci)
    {
        // notify
        ci.started();
        compactions.add(ci);
    }

    public void finishCompaction(CompactionInfo.Holder ci)
    {
        // notify
        ci.finished();
        compactions.remove(ci);
        bytesCompacted.inc(ci.getCompactionInfo().getTotal());
        totalCompactionsCompleted.mark();
    }

    public static List<CompactionInfo.Holder> getCompactions()
    {
        return new ArrayList<CompactionInfo.Holder>(compactions);
    }
}

@@ -4663,24 +4663,144 @@
 MetaData();%0A
+                    if (metaData == null)%0A                    %7B%0A                        continue;%0A                    %7D%0A
             

Fix non-fatal NPE in CompactionMetrics