Fix size allocation in IdMapBuilder#buildSparseNodeMapping

We need to allocate `highestNodeId + 1` to be able to store
an node with `id = highestNodeId`. The number of pages in
the HugeSparseLongArray if based on the size.

Co-authored-by: Max Kießling <[email protected]>

Author: s1ck

core/src/main/java/org/neo4j/graphalgo/core/loading/IdMapBuilder.java

@@ -57,7 +57,7 @@ static SparseNodeMapping buildSparseNodeMapping(
         int concurrency,
         AllocationTracker tracker
     ) {
-        SparseNodeMapping.Builder nodeMappingBuilder = SparseNodeMapping.Builder.create(highestNodeId == 0 ? 1 : highestNodeId, tracker);
+        SparseNodeMapping.Builder nodeMappingBuilder = SparseNodeMapping.Builder.create(highestNodeId + 1, tracker);
         ParallelUtil.readParallel(
                 concurrency,
                 graphIds.size(),

core/src/test/java/org/neo4j/graphalgo/core/loading/IdMapBuilderTest.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2017-2020 "Neo4j,"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Neo4j is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.neo4j.graphalgo.core.loading;
+
+import org.junit.jupiter.api.Test;
+import org.neo4j.graphalgo.core.utils.paged.AllocationTracker;
+import org.neo4j.graphalgo.core.utils.paged.HugeLongArray;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class IdMapBuilderTest {
+
+    @Test
+    void buildSparseNodeMappingWithPageSizeEntries() {
+        long nodeId = 4096; // equals the PAGE_SIZE in a HugeSparseLongArray
+
+        HugeLongArray hugeLongArray = HugeLongArray.newArray(1, AllocationTracker.EMPTY);
+        hugeLongArray.set(0, nodeId);
+
+        SparseNodeMapping hugeSparseLongArray = IdMapBuilder.buildSparseNodeMapping(
+            hugeLongArray,
+            nodeId,
+            1,
+            AllocationTracker.EMPTY
+        );
+
+        assertTrue(hugeSparseLongArray.contains(nodeId));
+    }
+}