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 * Licensed to the Apache Software Foundation (ASF) under one
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 * 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
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package org.apache.cassandra.db.lifecycle;

import java.util.*;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.base.Predicate;
import com.google.common.collect.*;

import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.Memtable;
import org.apache.cassandra.db.PartitionPosition;
import org.apache.cassandra.dht.AbstractBounds;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.utils.Interval;

import static com.google.common.base.Predicates.equalTo;
import static com.google.common.base.Predicates.not;
import static com.google.common.collect.ImmutableList.copyOf;
import static com.google.common.collect.ImmutableList.of;
import static com.google.common.collect.Iterables.all;
import static com.google.common.collect.Iterables.concat;
import static com.google.common.collect.Iterables.filter;
import static org.apache.cassandra.db.lifecycle.Helpers.emptySet;
import static org.apache.cassandra.db.lifecycle.Helpers.filterOut;
import static org.apache.cassandra.db.lifecycle.Helpers.replace;

An immutable structure holding the current memtable, the memtables pending
flush, the sstables for a column family, and the sstables that are active
in compaction (a subset of the sstables).
Modifications to instances are all performed via a Function produced by the static methods in this class.
These are composed as necessary and provided to the Tracker.apply() methods, which atomically reject or
accept and apply the changes to the View.
/**
 * An immutable structure holding the current memtable, the memtables pending
 * flush, the sstables for a column family, and the sstables that are active
 * in compaction (a subset of the sstables).
 *
 * Modifications to instances are all performed via a Function produced by the static methods in this class.
 * These are composed as necessary and provided to the Tracker.apply() methods, which atomically reject or
 * accept and apply the changes to the View.
 *
 */
public class View
{
    
ordinarily a list of size 1, but when preparing to flush will contain both the memtable we will flush
and the new replacement memtable, until all outstanding write operations on the old table complete.
The last item in the list is always the "current" memtable.
/**
     * ordinarily a list of size 1, but when preparing to flush will contain both the memtable we will flush
     * and the new replacement memtable, until all outstanding write operations on the old table complete.
     * The last item in the list is always the "current" memtable.
     */
    public final List<Memtable> liveMemtables;
    
contains all memtables that are no longer referenced for writing and are queued for / in the process of being
flushed. In chronologically ascending order.
/**
     * contains all memtables that are no longer referenced for writing and are queued for / in the process of being
     * flushed. In chronologically ascending order.
     */
    public final List<Memtable> flushingMemtables;
    final Set<SSTableReader> compacting;
    final Set<SSTableReader> sstables;
    // we use a Map here so that we can easily perform identity checks as well as equality checks.
    // When marking compacting, we now  indicate if we expect the sstables to be present (by default we do),
    // and we then check that not only are they all present in the live set, but that the exact instance present is
    // the one we made our decision to compact against.
    final Map<SSTableReader, SSTableReader> sstablesMap;
    final Map<SSTableReader, SSTableReader> compactingMap;

    final SSTableIntervalTree intervalTree;

    View(List<Memtable> liveMemtables, List<Memtable> flushingMemtables, Map<SSTableReader, SSTableReader> sstables, Map<SSTableReader, SSTableReader> compacting, SSTableIntervalTree intervalTree)
    {
        assert liveMemtables != null;
        assert flushingMemtables != null;
        assert sstables != null;
        assert compacting != null;
        assert intervalTree != null;

        this.liveMemtables = liveMemtables;
        this.flushingMemtables = flushingMemtables;

        this.sstablesMap = sstables;
        this.sstables = sstablesMap.keySet();
        this.compactingMap = compacting;
        this.compacting = compactingMap.keySet();
        this.intervalTree = intervalTree;
    }

    public Memtable getCurrentMemtable()
    {
        return liveMemtables.get(liveMemtables.size() - 1);
    }

    
Returns:
the active memtable and all the memtables that are pending flush./**
     * @return the active memtable and all the memtables that are pending flush.
     */
    public Iterable<Memtable> getAllMemtables()
    {
        return concat(flushingMemtables, liveMemtables);
    }

    // shortcut for all live sstables, so can efficiently use it for size, etc
    public Set<SSTableReader> liveSSTables()
    {
        return sstables;
    }

    public Iterable<SSTableReader> sstables(SSTableSet sstableSet, Predicate<SSTableReader> filter)
    {
        return filter(select(sstableSet), filter);
    }

    // any sstable known by this tracker in any form; we have a special method here since it's only used for testing/debug
    // (strong leak detection), and it does not follow the normal pattern
    @VisibleForTesting
    public Iterable<SSTableReader> allKnownSSTables()
    {
        return Iterables.concat(sstables, filterOut(compacting, sstables));
    }

    public Iterable<SSTableReader> select(SSTableSet sstableSet)
    {
        switch (sstableSet)
        {
            case LIVE:
                return sstables;
            case NONCOMPACTING:
                return filter(sstables, (s) -> !compacting.contains(s));
            case CANONICAL:
                Set<SSTableReader> canonicalSSTables = new HashSet<>();
                for (SSTableReader sstable : compacting)
                    if (sstable.openReason != SSTableReader.OpenReason.EARLY)
                        canonicalSSTables.add(sstable);
                // reason for checking if compacting contains the sstable is that if compacting has an EARLY version
                // of a NORMAL sstable, we still have the canonical version of that sstable in sstables.
                // note that the EARLY version is equal, but not == since it is a different instance of the same sstable.
                for (SSTableReader sstable : sstables)
                    if (!compacting.contains(sstable) && sstable.openReason != SSTableReader.OpenReason.EARLY)
                        canonicalSSTables.add(sstable);

                return canonicalSSTables;
            default:
                throw new IllegalStateException();
        }
    }

    public Iterable<SSTableReader> getUncompacting(Iterable<SSTableReader> candidates)
    {
        return filter(candidates, new Predicate<SSTableReader>()
        {
            public boolean apply(SSTableReader sstable)
            {
                return !compacting.contains(sstable);
            }
        });
    }

    public boolean isEmpty()
    {
        return sstables.isEmpty()
               && liveMemtables.size() <= 1
               && flushingMemtables.size() == 0
               && (liveMemtables.size() == 0 || liveMemtables.get(0).getOperations() == 0);
    }

    @Override
    public String toString()
    {
        return String.format("View(pending_count=%d, sstables=%s, compacting=%s)", liveMemtables.size() + flushingMemtables.size() - 1, sstables, compacting);
    }

    
Returns the sstables that have any partition between left and right, when both bounds are taken inclusively. The interval formed by left and right shouldn't wrap. /**
     * Returns the sstables that have any partition between {@code left} and {@code right}, when both bounds are taken inclusively.
     * The interval formed by {@code left} and {@code right} shouldn't wrap.
     */
    public Iterable<SSTableReader> liveSSTablesInBounds(PartitionPosition left, PartitionPosition right)
    {
        assert !AbstractBounds.strictlyWrapsAround(left, right);

        if (intervalTree.isEmpty())
            return Collections.emptyList();

        PartitionPosition stopInTree = right.isMinimum() ? intervalTree.max() : right;
        return intervalTree.search(Interval.create(left, stopInTree));
    }

    public static List<SSTableReader> sstablesInBounds(PartitionPosition left, PartitionPosition right, SSTableIntervalTree intervalTree)
    {
        assert !AbstractBounds.strictlyWrapsAround(left, right);

        if (intervalTree.isEmpty())
            return Collections.emptyList();

        PartitionPosition stopInTree = right.isMinimum() ? intervalTree.max() : right;
        return intervalTree.search(Interval.create(left, stopInTree));
    }

    public static Function<View, Iterable<SSTableReader>> selectFunction(SSTableSet sstableSet)
    {
        return (view) -> view.select(sstableSet);
    }

    public static Function<View, Iterable<SSTableReader>> select(SSTableSet sstableSet, Predicate<SSTableReader> filter)
    {
        return (view) -> view.sstables(sstableSet, filter);
    }

    
Returns:
a ViewFragment containing the sstables and memtables that may need to be merged
for the given @param key, according to the interval tree/**
     * @return a ViewFragment containing the sstables and memtables that may need to be merged
     * for the given @param key, according to the interval tree
     */
    public static Function<View, Iterable<SSTableReader>> select(SSTableSet sstableSet, DecoratedKey key)
    {
        assert sstableSet == SSTableSet.LIVE;
        return (view) -> view.intervalTree.search(key);
    }

    
Returns:
a ViewFragment containing the sstables and memtables that may need to be merged
for rows within @param rowBounds, inclusive, according to the interval tree./**
     * @return a ViewFragment containing the sstables and memtables that may need to be merged
     * for rows within @param rowBounds, inclusive, according to the interval tree.
     */
    public static Function<View, Iterable<SSTableReader>> selectLive(AbstractBounds<PartitionPosition> rowBounds)
    {
        // Note that View.sstablesInBounds always includes it's bound while rowBounds may not. This is ok however
        // because the fact we restrict the sstables returned by this function is an optimization in the first
        // place and the returned sstables will (almost) never cover *exactly* rowBounds anyway. It's also
        // *very* unlikely that a sstable is included *just* because we consider one of the bound inclusively
        // instead of exclusively, so the performance impact is negligible in practice.
        return (view) -> view.liveSSTablesInBounds(rowBounds.left, rowBounds.right);
    }

    // METHODS TO CONSTRUCT FUNCTIONS FOR MODIFYING A VIEW:

    // return a function to un/mark the provided readers compacting in a view
    static Function<View, View> updateCompacting(final Set<SSTableReader> unmark, final Iterable<SSTableReader> mark)
    {
        if (unmark.isEmpty() && Iterables.isEmpty(mark))
            return Functions.identity();
        return new Function<View, View>()
        {
            public View apply(View view)
            {
                assert all(mark, Helpers.idIn(view.sstablesMap));
                return new View(view.liveMemtables, view.flushingMemtables, view.sstablesMap,
                                replace(view.compactingMap, unmark, mark),
                                view.intervalTree);
            }
        };
    }

    // construct a predicate to reject views that do not permit us to mark these readers compacting;
    // i.e. one of them is either already compacting, has been compacted, or has been replaced
    static Predicate<View> permitCompacting(final Iterable<SSTableReader> readers)
    {
        return new Predicate<View>()
        {
            public boolean apply(View view)
            {
                for (SSTableReader reader : readers)
                    if (view.compacting.contains(reader) || view.sstablesMap.get(reader) != reader || reader.isMarkedCompacted())
                        return false;
                return true;
            }
        };
    }

    // construct a function to change the liveset in a Snapshot
    static Function<View, View> updateLiveSet(final Set<SSTableReader> remove, final Iterable<SSTableReader> add)
    {
        if (remove.isEmpty() && Iterables.isEmpty(add))
            return Functions.identity();
        return new Function<View, View>()
        {
            public View apply(View view)
            {
                Map<SSTableReader, SSTableReader> sstableMap = replace(view.sstablesMap, remove, add);
                return new View(view.liveMemtables, view.flushingMemtables, sstableMap, view.compactingMap,
                                SSTableIntervalTree.build(sstableMap.keySet()));
            }
        };
    }

    // called prior to initiating flush: add newMemtable to liveMemtables, making it the latest memtable
    static Function<View, View> switchMemtable(final Memtable newMemtable)
    {
        return new Function<View, View>()
        {
            public View apply(View view)
            {
                List<Memtable> newLive = ImmutableList.<Memtable>builder().addAll(view.liveMemtables).add(newMemtable).build();
                assert newLive.size() == view.liveMemtables.size() + 1;
                return new View(newLive, view.flushingMemtables, view.sstablesMap, view.compactingMap, view.intervalTree);
            }
        };
    }

    // called before flush: move toFlush from liveMemtables to flushingMemtables
    static Function<View, View> markFlushing(final Memtable toFlush)
    {
        return new Function<View, View>()
        {
            public View apply(View view)
            {
                List<Memtable> live = view.liveMemtables, flushing = view.flushingMemtables;
                List<Memtable> newLive = copyOf(filter(live, not(equalTo(toFlush))));
                List<Memtable> newFlushing = copyOf(concat(filter(flushing, lessThan(toFlush)),
                                                           of(toFlush),
                                                           filter(flushing, not(lessThan(toFlush)))));
                assert newLive.size() == live.size() - 1;
                assert newFlushing.size() == flushing.size() + 1;
                return new View(newLive, newFlushing, view.sstablesMap, view.compactingMap, view.intervalTree);
            }
        };
    }

    // called after flush: removes memtable from flushingMemtables, and inserts flushed into the live sstable set
    static Function<View, View> replaceFlushed(final Memtable memtable, final Iterable<SSTableReader> flushed)
    {
        return new Function<View, View>()
        {
            public View apply(View view)
            {
                List<Memtable> flushingMemtables = copyOf(filter(view.flushingMemtables, not(equalTo(memtable))));
                assert flushingMemtables.size() == view.flushingMemtables.size() - 1;

                if (flushed == null || Iterables.isEmpty(flushed))
                    return new View(view.liveMemtables, flushingMemtables, view.sstablesMap,
                                    view.compactingMap, view.intervalTree);

                Map<SSTableReader, SSTableReader> sstableMap = replace(view.sstablesMap, emptySet(), flushed);
                return new View(view.liveMemtables, flushingMemtables, sstableMap, view.compactingMap,
                                SSTableIntervalTree.build(sstableMap.keySet()));
            }
        };
    }

    private static <T extends Comparable<T>> Predicate<T> lessThan(final T lessThan)
    {
        return new Predicate<T>()
        {
            public boolean apply(T t)
            {
                return t.compareTo(lessThan) < 0;
            }
        };
    }
}