cache last used date prefix

The 99.9999% use case is to ingest data
from the same month.

data-store/src/main/java/org/lucares/pdb/datastore/internal/DateIndexExtension.java

@@ -13,6 +13,7 @@ import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.ConcurrentNavigableMap;
 import java.util.concurrent.ConcurrentSkipListMap;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.lucares.pdb.api.DateTimeRange;
 
@@ -26,6 +27,8 @@ public class DateIndexExtension {
 	// visible for test
 	static final ConcurrentNavigableMap<Long, DatePrefixAndRange> DATE_PREFIX_CACHE = new ConcurrentSkipListMap<>();
 
+	private static final AtomicReference<DatePrefixAndRange> LAST_ACCESSED = new AtomicReference<>(null);
+
 	static Set<String> toDateIndexPrefix(final DateTimeRange dateRange) {
 		final Set<String> result = new TreeSet<>();
 
@@ -46,18 +49,24 @@ public class DateIndexExtension {
 	}
 
 	public static ParititionId toPartitionId(final long epochMilli) {
-		// TODO most calls will be for a similar date -> add a shortcut
+		String result;
+		final DatePrefixAndRange lastAccessed = LAST_ACCESSED.get();
+		if (lastAccessed != null && lastAccessed.getMinEpochMilli() <= epochMilli
+				&& lastAccessed.getMaxEpochMilli() >= epochMilli) {
+			result = lastAccessed.getDatePrefix();
+		} else {
 			final Entry<Long, DatePrefixAndRange> value = DATE_PREFIX_CACHE.floorEntry(epochMilli);
 
-		String result;
 			if (value == null || !value.getValue().contains(epochMilli)) {
 				final DatePrefixAndRange newValue = toDatePrefixAndRange(epochMilli);
 				DATE_PREFIX_CACHE.put(newValue.getMinEpochMilli(), newValue);
 				result = newValue.getDatePrefix();
+				LAST_ACCESSED.set(newValue);
 			} else {
 				result = value.getValue().getDatePrefix();
+				LAST_ACCESSED.set(value.getValue());
+			}
 		}
-
 		return new ParititionId(result);
 	}
 

data-store/src/test/java/org/lucares/pdb/datastore/internal/DateIndexExtensionTest.java

@@ -4,6 +4,7 @@ import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.DoubleSummaryStatistics;
 import java.util.List;
 import java.util.Set;
 
@@ -79,11 +80,13 @@ public class DateIndexExtensionTest {
 		final DateTimeRange range_201712_201801 = new DateTimeRange(mid_201712, min_201801);
 		final DateTimeRange range_201712_201712 = new DateTimeRange(mid_201712, mid_201712);
 
-		final List<ParititionId> dateIndexPrefixesWithEmptyCache = DateIndexExtension.toPartitionIds(range_201712_201802);
+		final List<ParititionId> dateIndexPrefixesWithEmptyCache = DateIndexExtension
+				.toPartitionIds(range_201712_201802);
 		Assert.assertEquals(dateIndexPrefixesWithEmptyCache,
 				Arrays.asList(new ParititionId("201712"), new ParititionId("201801"), new ParititionId("201802")));
 
-		final List<ParititionId> dateIndexPrefixesWithFilledCache = DateIndexExtension.toPartitionIds(range_201712_201801);
+		final List<ParititionId> dateIndexPrefixesWithFilledCache = DateIndexExtension
+				.toPartitionIds(range_201712_201801);
 		Assert.assertEquals(dateIndexPrefixesWithFilledCache,
 				Arrays.asList(new ParititionId("201712"), new ParititionId("201801")));
 
@@ -103,4 +106,39 @@ public class DateIndexExtensionTest {
 				.toDateIndexEpochMillis(new DateTimeRange(mid_201712, min_201802));
 		Assert.assertEquals(dateIndexEpochMillis, Arrays.asList(exp_201712, exp_201801, exp_201802));
 	}
+
+	public void testPerformance() {
+
+		final long min = OffsetDateTime.of(2010, 1, 1, 0, 0, 0, 0, ZoneOffset.UTC).toInstant().toEpochMilli();
+		final long mid = OffsetDateTime.of(2020, 6, 1, 0, 0, 0, 0, ZoneOffset.UTC).toInstant().toEpochMilli();
+		final long max = OffsetDateTime.of(2030, 12, 31, 0, 0, 0, 0, ZoneOffset.UTC).toInstant().toEpochMilli();
+
+		final int iterations = 1_000_000;
+		final int factor = 1;
+		final int warmup = 20 * factor;
+		final int rounds = warmup + 20;
+
+		// fill the cache
+		DateIndexExtension.DATE_PREFIX_CACHE.clear();
+		for (long i = min; i < max; i += 3600 * 24 * 28) {
+			DateIndexExtension.toPartitionId(i);
+		}
+
+		final List<Double> measurements = new ArrayList<>();
+
+		for (int r = 0; r < rounds; r++) {
+
+			final long start = System.nanoTime();
+			for (int i = 0; i < iterations; i++) {
+				DateIndexExtension.toPartitionId(mid);
+			}
+			final double duration = (System.nanoTime() - start) / 1_000_000.0;
+			System.out.println("duration: " + duration + "ms");
+			measurements.add(duration);
+		}
+
+		final DoubleSummaryStatistics stats = measurements.subList(warmup, rounds).stream().mapToDouble(d -> factor * d)
+				.summaryStatistics();
+		System.out.println(stats);
+	}
 }