cassandra-trunk/src/java/org/apache/cassandra/tools/SSTableExpiredBlockers.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.tools;

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.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.SSTableFormat.Components;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.schema.Schema;
import org.apache.cassandra.schema.TableMetadata;

import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;

/**
 * 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)
    {
        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();

        TableMetadata metadata = Schema.instance.validateTable(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(cfs, sstable.getKey());
                    sstables.add(reader);
                }
                catch (Throwable t)
                {
                    out.println("Couldn't open sstable: " + sstable.getKey().fileFor(Components.DATA) + " (" + t.getMessage() + ")");
                }
            }
        }
        if (sstables.isEmpty())
        {
            out.println("No sstables for " + keyspace + "." + columnfamily);
            System.exit(1);
        }

        long gcBefore = (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, long 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();
    }
}
