introduce index clustering (part 1)

In order to prevent files from getting too big and
make it easier to implement retention policies, we
are splitting all files into chunks. Each chunk
contains the data for a time interval (1 month per
default).
This first changeset introduces the ClusteredPersistentMap
that implements this for PersistentMap. It is used
for a couple (not all) of indices.

pdb-api/src/test/java/org/lucares/pdb/api/DateTimeRangeTest.java

@@ -0,0 +1,37 @@
+package org.lucares.pdb.api;
+
+import java.time.Instant;
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.testng.Assert;
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+public class DateTimeRangeTest {
+	@DataProvider
+	Object[][] providerIntersect() {
+		final List<Object[]> result = new ArrayList<>();
+
+		final OffsetDateTime a = Instant.ofEpochMilli(1000).atOffset(ZoneOffset.UTC);
+		final OffsetDateTime b = Instant.ofEpochMilli(2000).atOffset(ZoneOffset.UTC);
+		final OffsetDateTime c = Instant.ofEpochMilli(3000).atOffset(ZoneOffset.UTC);
+		final OffsetDateTime d = Instant.ofEpochMilli(4000).atOffset(ZoneOffset.UTC);
+
+		result.add(new Object[] { new DateTimeRange(a, b), new DateTimeRange(c, d), false });
+		result.add(new Object[] { new DateTimeRange(a, c), new DateTimeRange(b, d), true });
+		result.add(new Object[] { new DateTimeRange(a, d), new DateTimeRange(b, d), true });
+		result.add(new Object[] { new DateTimeRange(a, d), new DateTimeRange(b, d), true });
+		result.add(new Object[] { new DateTimeRange(a, b), new DateTimeRange(b, d), true });
+
+		return result.toArray(new Object[result.size()][]);
+	}
+
+	@Test(dataProvider = "providerIntersect")
+	public void testIntersect(final DateTimeRange a, final DateTimeRange b, final boolean expected) throws Exception {
+		Assert.assertEquals(a.intersect(b), expected, a + " intersects " + b);
+		Assert.assertEquals(b.intersect(a), expected, a + " intersects " + b);
+	}
+}