Restore date aggregation performance in UTC case

The benchmarks showed a sharp decrease in aggregation performance for
the UTC case.

This commit uses the same calculation as joda time, which requires no
conversion into any java time object, also, the check for an fixedoffset
has been put into the ctor to reduce the need for runtime calculations.
The same goes for the amount of the used unit in milliseconds.

Closes elastic#37826

benchmarks/src/main/java/org/elasticsearch/benchmark/time/RoundingBenchmark.java

@@ -34,8 +34,11 @@
 import org.openjdk.jmh.annotations.Warmup;
 
 import java.time.ZoneId;
+import java.time.ZoneOffset;
 import java.util.concurrent.TimeUnit;
 
+import static org.elasticsearch.common.Rounding.DateTimeUnit.DAY_OF_MONTH;
+
 @Fork(3)
 @Warmup(iterations = 10)
 @Measurement(iterations = 10)
@@ -48,23 +51,13 @@ public class RoundingBenchmark {
     private final ZoneId zoneId = ZoneId.of("Europe/Amsterdam");
     private final DateTimeZone timeZone = DateUtils.zoneIdToDateTimeZone(zoneId);
 
+    private final long timestamp = 1548879021354L;
+
     private final org.elasticsearch.common.rounding.Rounding jodaRounding =
-            org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.HOUR_OF_DAY).timeZone(timeZone).build();
+        org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.HOUR_OF_DAY).timeZone(timeZone).build();
     private final Rounding javaRounding = Rounding.builder(Rounding.DateTimeUnit.HOUR_OF_DAY)
         .timeZone(zoneId).build();
 
-    private final org.elasticsearch.common.rounding.Rounding jodaDayOfMonthRounding =
-            org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.DAY_OF_MONTH).timeZone(timeZone).build();
-    private final Rounding javaDayOfMonthRounding = Rounding.builder(TimeValue.timeValueMinutes(60))
-        .timeZone(zoneId).build();
-
-    private final org.elasticsearch.common.rounding.Rounding timeIntervalRoundingJoda =
-            org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.DAY_OF_MONTH).timeZone(timeZone).build();
-    private final Rounding timeIntervalRoundingJava = Rounding.builder(TimeValue.timeValueMinutes(60))
-        .timeZone(zoneId).build();
-
-    private final long timestamp = 1548879021354L;
-
     @Benchmark
     public long timeRoundingDateTimeUnitJoda() {
         return jodaRounding.round(timestamp);
@@ -75,6 +68,11 @@ public long timeRoundingDateTimeUnitJava() {
         return javaRounding.round(timestamp);
     }
 
+    private final org.elasticsearch.common.rounding.Rounding jodaDayOfMonthRounding =
+        org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.DAY_OF_MONTH).timeZone(timeZone).build();
+    private final Rounding javaDayOfMonthRounding = Rounding.builder(DAY_OF_MONTH)
+        .timeZone(zoneId).build();
+
     @Benchmark
     public long timeRoundingDateTimeUnitDayOfMonthJoda() {
         return jodaDayOfMonthRounding.round(timestamp);
@@ -85,6 +83,11 @@ public long timeRoundingDateTimeUnitDayOfMonthJava() {
         return javaDayOfMonthRounding.round(timestamp);
     }
 
+    private final org.elasticsearch.common.rounding.Rounding timeIntervalRoundingJoda =
+        org.elasticsearch.common.rounding.Rounding.builder(TimeValue.timeValueMinutes(60)).timeZone(timeZone).build();
+    private final Rounding timeIntervalRoundingJava = Rounding.builder(TimeValue.timeValueMinutes(60))
+        .timeZone(zoneId).build();
+
     @Benchmark
     public long timeIntervalRoundingJava() {
         return timeIntervalRoundingJava.round(timestamp);
@@ -94,4 +97,19 @@ public long timeIntervalRoundingJava() {
     public long timeIntervalRoundingJoda() {
         return timeIntervalRoundingJoda.round(timestamp);
     }
+
+    private final org.elasticsearch.common.rounding.Rounding timeUnitRoundingUtcMonthOfYearJoda =
+        org.elasticsearch.common.rounding.Rounding.builder(DateTimeUnit.DAY_OF_MONTH).timeZone(DateTimeZone.UTC).build();
+    private final Rounding timeUnitRoundingUtcMonthOfYearJava = Rounding.builder(DAY_OF_MONTH)
+        .timeZone(ZoneOffset.UTC).build();
+
+    @Benchmark
+    public long timeUnitRoundingUtcMonthOfYearJava() {
+        return timeUnitRoundingUtcMonthOfYearJava.round(timestamp);
+    }
+
+    @Benchmark
+    public long timeUnitRoundingUtcMonthOfYearJoda() {
+        return timeUnitRoundingUtcMonthOfYearJoda.round(timestamp);
+    }
 }

server/src/main/java/org/elasticsearch/common/Rounding.java

@@ -70,10 +70,16 @@ public enum DateTimeUnit {
 
         private final byte id;
         private final TemporalField field;
+        private final long unitMillis;
 
         DateTimeUnit(byte id, TemporalField field) {
             this.id = id;
             this.field = field;
+            this.unitMillis = field.getBaseUnit().getDuration().toMillis();
+        }
+
+        public long getUnitMillis() {
+            return unitMillis;
         }
 
         public byte getId() {
@@ -182,12 +188,14 @@ static class TimeUnitRounding extends Rounding {
         private final DateTimeUnit unit;
         private final ZoneId timeZone;
         private final boolean unitRoundsToMidnight;
+        private final boolean isFixedOffset;
 
 
         TimeUnitRounding(DateTimeUnit unit, ZoneId timeZone) {
             this.unit = unit;
             this.timeZone = timeZone;
             this.unitRoundsToMidnight = this.unit.field.getBaseUnit().getDuration().toMillis() > 3600000L;
+            this.isFixedOffset = timeZone.getRules().isFixedOffset();
         }
 
         TimeUnitRounding(StreamInput in) throws IOException {
@@ -236,7 +244,20 @@ private LocalDateTime truncateLocalDateTime(LocalDateTime localDateTime) {
         }
 
         @Override
-        public long round(final long utcMillis) {
+        public long round(long utcMillis) {
+            // this works as long as the offset doesn't change.  It is worth getting this case out of the way first, as
+            // the calculations for fixing things near to offset changes are a little expensive and are unnecessary in the common case
+            // of working in UTC.
+            if (isFixedOffset) {
+                long unitMillis = unit.getUnitMillis();
+                if (utcMillis >= 0) {
+                    return utcMillis - utcMillis % unitMillis;
+                } else {
+                    utcMillis += 1;
+                    return utcMillis - utcMillis % unitMillis - unitMillis;
+                }
+            }
+
             Instant instant = Instant.ofEpochMilli(utcMillis);
             if (unitRoundsToMidnight) {
                 final LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, timeZone);