org.neo4j.storageengine.api.schema.IndexSampler Maven / Gradle / Ivy

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/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.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.storageengine.api.schema;

import org.neo4j.kernel.api.exceptions.index.IndexNotFoundKernelException;
import org.neo4j.register.Register;

/**
 * Component able to sample schema index.
 */
public interface IndexSampler
{
    IndexSampler EMPTY = result -> {
        result.write( 0, 0 );
        return 0;
    };

    /**
     * Sample this index (on the current thread)
     *
     * @param result contains the unique values and the sampled size
     * @return the index size
     * @throws IndexNotFoundKernelException if the index is dropped while sampling
     */
    long sampleIndex( Register.DoubleLong.Out result ) throws IndexNotFoundKernelException;
}