org.neo4j.kernel.impl.index.schema.DeferredConflictCheckingIndexUpdater Maven / Gradle / Ivy

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/*
 * Copyright (c) 2018-2020 "Graph Foundation,"
 * Graph Foundation, Inc. [https://graphfoundation.org]
 *
 * This file is part of ONgDB.
 *
 * ONgDB is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
/*
 * Copyright (c) 2002-2020 "Neo4j,"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.index.schema;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
import java.util.function.Supplier;

import org.neo4j.collection.primitive.PrimitiveLongResourceIterator;
import org.neo4j.internal.kernel.api.IndexQuery;
import org.neo4j.kernel.api.exceptions.index.IndexEntryConflictException;
import org.neo4j.kernel.api.exceptions.index.IndexNotApplicableKernelException;
import org.neo4j.kernel.api.index.IndexEntryUpdate;
import org.neo4j.kernel.api.index.IndexUpdater;
import org.neo4j.kernel.api.schema.index.SchemaIndexDescriptor;
import org.neo4j.storageengine.api.schema.IndexReader;
import org.neo4j.values.storable.ValueTuple;

import static org.neo4j.internal.kernel.api.IndexQuery.exact;
import static org.neo4j.kernel.impl.api.index.UpdateMode.REMOVED;

/**
 * This deferring conflict checker solves e.g. a problem of applying updates to an index that is aware of,
 * and also prevents, duplicates while applying. Consider this scenario:
 *
 *  *    GIVEN:
 *    Node A w/ property value P
 *    Node B w/ property value Q
 *
 *    WHEN Applying a transaction that:
 *    Sets A property value to Q
 *    Deletes B
 * 
 *
 * Then an index that is conscious about conflicts when applying may see intermediary conflicts,
 * depending on the order in which updates are applied. Remembering which value tuples have been altered and
 * checking conflicts for those in {@link #close()} works around that problem.
 *
 * This updater wrapping should only be used in specific places to solve specific problems, not generally
 * when applying updates to online indexes.
 */
public class DeferredConflictCheckingIndexUpdater implements IndexUpdater
{
    private final IndexUpdater actual;
    private final Supplier readerSupplier;
    private final SchemaIndexDescriptor schemaIndexDescriptor;
    private final Set touchedTuples = new HashSet<>();

    public DeferredConflictCheckingIndexUpdater( IndexUpdater actual, Supplier readerSupplier, SchemaIndexDescriptor schemaIndexDescriptor )
    {
        this.actual = actual;
        this.readerSupplier = readerSupplier;
        this.schemaIndexDescriptor = schemaIndexDescriptor;
    }

    @Override
    public void process( IndexEntryUpdate update ) throws IOException, IndexEntryConflictException
    {
        actual.process( update );
        if ( update.updateMode() != REMOVED )
        {
            touchedTuples.add( ValueTuple.of( update.values() ) );
        }
    }

    @Override
    public void close() throws IOException, IndexEntryConflictException
    {
        actual.close();
        try ( IndexReader reader = readerSupplier.get() )
        {
            for ( ValueTuple tuple : touchedTuples )
            {
                try ( PrimitiveLongResourceIterator results = reader.query( queryOf( tuple ) ) )
                {
                    if ( results.hasNext() )
                    {
                        long firstEntityId = results.next();
                        if ( results.hasNext() )
                        {
                            long secondEntityId = results.next();
                            throw new IndexEntryConflictException( firstEntityId, secondEntityId, tuple );
                        }
                    }
                }
            }
        }
        catch ( IndexNotApplicableKernelException e )
        {
            throw new IllegalArgumentException( "Unexpectedly the index reader couldn't handle this query", e );
        }
    }

    private IndexQuery[] queryOf( ValueTuple tuple )
    {
        IndexQuery[] predicates = new IndexQuery[tuple.size()];
        int[] propertyIds = schemaIndexDescriptor.schema().getPropertyIds();
        for ( int i = 0; i < predicates.length; i++ )
        {
            predicates[i] = exact( propertyIds[i], tuple.valueAt( i ) );
        }
        return predicates;
    }
}