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 * 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.tools;

import java.io.IOException;
import java.io.PrintStream;
import java.util.Collections;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;

import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.config.Schema;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.Directories;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.io.sstable.Component;
import org.apache.cassandra.io.sstable.Descriptor;
import org.apache.cassandra.io.sstable.format.SSTableReader;

During compaction we can drop entire sstables if they only contain expired tombstones and if it is guaranteed
to not cover anything in other sstables. An expired sstable can be blocked from getting dropped if its newest
timestamp is newer than the oldest data in another sstable.
This class outputs all sstables that are blocking other sstables from getting dropped so that a user can
figure out why certain sstables are still on disk.
/**
 * During compaction we can drop entire sstables if they only contain expired tombstones and if it is guaranteed
 * to not cover anything in other sstables. An expired sstable can be blocked from getting dropped if its newest
 * timestamp is newer than the oldest data in another sstable.
 *
 * This class outputs all sstables that are blocking other sstables from getting dropped so that a user can
 * figure out why certain sstables are still on disk.
 */
public class SSTableExpiredBlockers
{
    public static void main(String[] args) throws IOException
    {
        PrintStream out = System.out;
        if (args.length < 2)
        {
            out.println("Usage: sstableexpiredblockers <keyspace> <table>");
            System.exit(1);
        }

        Util.initDatabaseDescriptor();

        String keyspace = args[args.length - 2];
        String columnfamily = args[args.length - 1];
        Schema.instance.loadFromDisk(false);

        CFMetaData metadata = Schema.instance.getCFMetaData(keyspace, columnfamily);
        if (metadata == null)
            throw new IllegalArgumentException(String.format("Unknown keyspace/table %s.%s",
                    keyspace,
                    columnfamily));

        Keyspace ks = Keyspace.openWithoutSSTables(keyspace);
        ColumnFamilyStore cfs = ks.getColumnFamilyStore(columnfamily);
        Directories.SSTableLister lister = cfs.getDirectories().sstableLister(Directories.OnTxnErr.THROW).skipTemporary(true);
        Set<SSTableReader> sstables = new HashSet<>();
        for (Map.Entry<Descriptor, Set<Component>> sstable : lister.list().entrySet())
        {
            if (sstable.getKey() != null)
            {
                try
                {
                    SSTableReader reader = SSTableReader.open(sstable.getKey());
                    sstables.add(reader);
                }
                catch (Throwable t)
                {
                    out.println("Couldn't open sstable: " + sstable.getKey().filenameFor(Component.DATA)+" ("+t.getMessage()+")");
                }
            }
        }
        if (sstables.isEmpty())
        {
            out.println("No sstables for " + keyspace + "." + columnfamily);
            System.exit(1);
        }

        int gcBefore = (int)(System.currentTimeMillis()/1000) - metadata.params.gcGraceSeconds;
        Multimap<SSTableReader, SSTableReader> blockers = checkForExpiredSSTableBlockers(sstables, gcBefore);
        for (SSTableReader blocker : blockers.keySet())
        {
            out.println(String.format("%s blocks %d expired sstables from getting dropped: %s%n",
                                    formatForExpiryTracing(Collections.singleton(blocker)),
                                    blockers.get(blocker).size(),
                                    formatForExpiryTracing(blockers.get(blocker))));
        }

        System.exit(0);
    }

    public static Multimap<SSTableReader, SSTableReader> checkForExpiredSSTableBlockers(Iterable<SSTableReader> sstables, int gcBefore)
    {
        Multimap<SSTableReader, SSTableReader> blockers = ArrayListMultimap.create();
        for (SSTableReader sstable : sstables)
        {
            if (sstable.getSSTableMetadata().maxLocalDeletionTime < gcBefore)
            {
                for (SSTableReader potentialBlocker : sstables)
                {
                    if (!potentialBlocker.equals(sstable) &&
                        potentialBlocker.getMinTimestamp() <= sstable.getMaxTimestamp() &&
                        potentialBlocker.getSSTableMetadata().maxLocalDeletionTime > gcBefore)
                        blockers.put(potentialBlocker, sstable);
                }
            }
        }
        return blockers;
    }

    private static String formatForExpiryTracing(Iterable<SSTableReader> sstables)
    {
        StringBuilder sb = new StringBuilder();

        for (SSTableReader sstable : sstables)
            sb.append(String.format("[%s (minTS = %d, maxTS = %d, maxLDT = %d)]", sstable, sstable.getMinTimestamp(), sstable.getMaxTimestamp(), sstable.getSSTableMetadata().maxLocalDeletionTime)).append(", ");

        return sb.toString();
    }
}