cassandra-trunk/test/microbench/org/apache/cassandra/test/microbench/DirectorySizerBench.java
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 * 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
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 * Unless required by applicable law or agreed to in writing, software
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 * See the License for the specific language governing permissions and
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package org.apache.cassandra.test.microbench;

import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.util.UUID;
import java.util.concurrent.TimeUnit;

import org.apache.cassandra.io.util.File;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.utils.DirectorySizeCalculator;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@Warmup(iterations = 1)
@Measurement(iterations = 30)
@Fork(value = 1, jvmArgsAppend = "-Xmx512M")
@Threads(1)
@State(Scope.Benchmark)
public class DirectorySizerBench
{
    private File tempDir;
    private DirectorySizeCalculator sizer;

    @Setup(Level.Trial)
    public void setUp() throws IOException
    {
        tempDir = new File(Files.createTempDirectory(randString()));

        // Since #'s on laptops and commodity desktops are so useful in considering enterprise virtualized server environments...

        // Spinning disk 7200rpm 1TB, win10, ntfs, i6600 skylake, 256 files:
        // [java] Result: 0.581 ▒(99.9%) 0.003 ms/op [Average]
        // [java]   Statistics: (min, avg, max) = (0.577, 0.581, 0.599), stdev = 0.005
        // [java]   Confidence interval (99.9%): [0.577, 0.584]

        // Same hardware, 25600 files:
        // [java] Result: 56.990 ▒(99.9%) 0.374 ms/op [Average]
        // [java]   Statistics: (min, avg, max) = (56.631, 56.990, 59.829), stdev = 0.560
        // [java]   Confidence interval (99.9%): [56.616, 57.364]

        // #'s on a rmbp, 2014, SSD, ubuntu 15.10, ext4, i7-4850HQ @ 2.3, 25600 samples
        // [java] Result: 74.714 ±(99.9%) 0.558 ms/op [Average]
        // [java]   Statistics: (min, avg, max) = (73.687, 74.714, 76.872), stdev = 0.835
        // [java]   Confidence interval (99.9%): [74.156, 75.272]

        // Test w/25,600 files, 100x the load of a full default CommitLog (8192) divided by size (32 per)
        populateRandomFiles(tempDir, 25600);
        sizer = new DirectorySizeCalculator();
    }

    @TearDown
    public void tearDown()
    {
        FileUtils.deleteRecursive(tempDir);
    }

    private void populateRandomFiles(File dir, int count) throws IOException
    {
        for (int i = 0; i < count; i++)
        {
            PrintWriter pw = new PrintWriter(dir + File.pathSeparator() + randString(), "UTF-8");
            pw.write(randString());
            pw.close();
        }
    }

    private String randString()
    {
        return UUID.randomUUID().toString();
    }

    @Benchmark
    public void countFiles(final Blackhole bh) throws IOException
    {
        Files.walkFileTree(tempDir.toPath(), sizer);
    }
}
