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PostgreSQL JDBC Driver - benchmarks
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/*
 * Copyright (c) 2003, PostgreSQL Global Development Group
 * See the LICENSE file in the project root for more information.
 */

package org.postgresql.benchmark.time;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.sql.Timestamp;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;
import java.util.concurrent.TimeUnit;

@Fork(value = 1, jvmArgsPrepend = "-Xmx128m")
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class TimestampToDate {
  private static final long ONEDAY = TimeUnit.DAYS.toMillis(1);

  @Param({"GMT+02:00", "Europe/Moscow"})
  String tz;
  TimeZone timeZone;

  Timestamp ts = new Timestamp(System.currentTimeMillis());
  Calendar cachedCalendar = new GregorianCalendar();

  @Setup
  public void init() {
    timeZone = TimeZone.getTimeZone(tz);
  }

  @Benchmark
  public long simple() {
    long millis = ts.getTime() + 10;
    ts.setTime(millis);
    Calendar cal = cachedCalendar;
    cal.setTimeZone(timeZone);
    cal.setTimeInMillis(millis);
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.set(Calendar.MINUTE, 0);
    cal.set(Calendar.SECOND, 0);
    cal.set(Calendar.MILLISECOND, 0);
    return cal.getTimeInMillis();
  }

  private static boolean isSimpleTimeZone(String id) {
    return id.startsWith("GMT") || id.startsWith("UTC");
  }

  @Benchmark
  public long advanced() {
    long millis = ts.getTime() + 10;
    TimeZone tz = this.timeZone;
    if (isSimpleTimeZone(tz.getID())) {
      // Truncate to 00:00 of the day.
      // Suppose the input date is 7 Jan 15:40 GMT+02:00 (that is 13:40 UTC)
      // We want it to become 7 Jan 00:00 GMT+02:00
      // 1) Make sure millis becomes 15:40 in UTC, so add offset
      int offset = tz.getRawOffset();
      millis += offset;
      // 2) Truncate hours, minutes, etc. Day is always 86400 seconds, no matter what leap seconds are
      millis = millis / ONEDAY * ONEDAY;
      // 2) Now millis is 7 Jan 00:00 UTC, however we need that in GMT+02:00, so subtract some offset
      millis -= offset;
      // Now we have brand-new 7 Jan 00:00 GMT+02:00
      return millis;
    }
    Calendar cal = cachedCalendar;
    cal.setTimeZone(tz);
    cal.setTimeInMillis(millis);
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.set(Calendar.MINUTE, 0);
    cal.set(Calendar.SECOND, 0);
    cal.set(Calendar.MILLISECOND, 0);
    return cal.getTimeInMillis();
  }

  public static void main(String[] args) throws RunnerException {
    Options opt = new OptionsBuilder()
        .include(TimestampToDate.class.getSimpleName())
        //.addProfiler(GCProfiler.class)
        //.addProfiler(FlightRecorderProfiler.class)
        .detectJvmArgs()
        .build();

    new Runner(opt).run();
  }

}