working on new ID based join iterator

Author: hmottestad

core/sail/lmdb/src/test/java/org/eclipse/rdf4j/sail/lmdb/QueryBenchmarkTest.java

@@ -221,6 +221,18 @@ public void orderedUnionLimitQueryProducesExpectedCount() {
 		}
 	}
 
+	@Test
+	@Timeout(30)
+	public void long_chain() {
+		try (SailRepositoryConnection connection = repository.getConnection()) {
+			long count;
+			try (var stream = connection.prepareTupleQuery(long_chain).evaluate().stream()) {
+				count = stream.count();
+			}
+//			assertEquals(???, count);
+		}
+	}
+
 	@Test
 	@Timeout(30)
 	public void subSelectQueryProducesExpectedCount() {

core/sail/lmdb/src/test/java/org/eclipse/rdf4j/sail/lmdb/join/LmdbIdMergeJoinIteratorTest.java

@@ -0,0 +1,85 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Eclipse RDF4J contributors.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Distribution License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *******************************************************************************/
+package org.eclipse.rdf4j.sail.lmdb.join;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+
+import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
+import org.eclipse.rdf4j.query.algebra.StatementPattern;
+import org.eclipse.rdf4j.query.algebra.Var;
+import org.eclipse.rdf4j.sail.lmdb.IdBindingInfo;
+import org.eclipse.rdf4j.sail.lmdb.RecordIterator;
+import org.eclipse.rdf4j.sail.lmdb.model.LmdbValue;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Isolated;
+
+@Isolated
+class LmdbIdMergeJoinIteratorTest {
+
+	@Test
+	void mergeJoinProducesIdRecordsWithoutMaterialization() throws Exception {
+		StatementPattern leftPattern = new StatementPattern(
+				new Var("x"),
+				new Var("pl", SimpleValueFactory.getInstance().createIRI("urn:p:left")),
+				new Var("ol", SimpleValueFactory.getInstance().createIRI("urn:o:left")));
+		StatementPattern rightPattern = new StatementPattern(
+				new Var("x"),
+				new Var("pr", SimpleValueFactory.getInstance().createIRI("urn:p:right")),
+				new Var("or", SimpleValueFactory.getInstance().createIRI("urn:o:right")));
+
+		LmdbIdJoinIterator.PatternInfo leftInfo = LmdbIdJoinIterator.PatternInfo.create(leftPattern);
+		LmdbIdJoinIterator.PatternInfo rightInfo = LmdbIdJoinIterator.PatternInfo.create(rightPattern);
+		IdBindingInfo bindingInfo = IdBindingInfo.combine(IdBindingInfo.fromFirstPattern(leftInfo), rightInfo, null);
+
+		long[] leftRecord = new long[] { 7L, LmdbValue.UNKNOWN_ID, LmdbValue.UNKNOWN_ID, 0L };
+		long[] rightRecord = new long[] { 7L, LmdbValue.UNKNOWN_ID, LmdbValue.UNKNOWN_ID, 0L };
+
+		RecordIterator leftIterator = new ArrayRecordIterator(leftRecord);
+		RecordIterator rightIterator = new ArrayRecordIterator(rightRecord);
+
+		LmdbIdMergeJoinIterator iterator = new LmdbIdMergeJoinIterator(leftIterator, rightIterator, leftInfo, rightInfo,
+				"x", bindingInfo);
+		try {
+			Object record = iterator.next();
+			assertThat(record).isInstanceOf(long[].class);
+			assertThat((long[]) record).containsExactly(7L, LmdbValue.UNKNOWN_ID, LmdbValue.UNKNOWN_ID, 0L);
+		} finally {
+			iterator.close();
+		}
+	}
+
+	private static final class ArrayRecordIterator implements RecordIterator {
+		private final long[][] data;
+		private int index;
+
+		private ArrayRecordIterator(long[]... records) {
+			this.data = Arrays.stream(records)
+					.map(arr -> Arrays.copyOf(arr, arr.length))
+					.toArray(long[][]::new);
+		}
+
+		@Override
+		public long[] next() {
+			if (index >= data.length) {
+				return null;
+			}
+			long[] source = data[index++];
+			return Arrays.copyOf(source, source.length);
+		}
+
+		@Override
+		public void close() {
+			// nothing to do
+		}
+	}
+}