HHH-18818 Fix ID conflicts between CTE batch inserts and PooledOptimi…

…zer sequence allocation

hibernate-core/src/main/java/org/hibernate/query/sqm/mutation/internal/cte/CteInsertHandler.java

@@ -20,6 +20,7 @@
 import org.hibernate.id.BulkInsertionCapableIdentifierGenerator;
 import org.hibernate.id.OptimizableGenerator;
 import org.hibernate.id.enhanced.Optimizer;
+import org.hibernate.id.enhanced.PooledOptimizer;
 import org.hibernate.internal.util.collections.CollectionHelper;
 import org.hibernate.internal.util.collections.Stack;
 import org.hibernate.metamodel.mapping.BasicValuedMapping;
@@ -387,7 +388,14 @@ public int execute(DomainQueryExecutionContext executionContext) {
 				rowsWithSequenceQuery.getSelectClause().addSqlSelection(
 						new SqlSelectionImpl(
 								1,
-								new SelfRenderingSqlFragmentExpression( fragment )
+								optimizer instanceof PooledOptimizer ?
+										new BinaryArithmeticExpression(
+												new SelfRenderingSqlFragmentExpression( fragment ),
+												BinaryArithmeticOperator.SUBTRACT,
+												new QueryLiteral<>( optimizer.getIncrementSize() - 1, integerType ),
+												integerType
+										) :
+										new SelfRenderingSqlFragmentExpression( fragment )
 						)
 				);
 				rowsWithSequenceQuery.applyPredicate(

hibernate-core/src/test/java/org/hibernate/orm/test/id/CteInsertStrategyWithPooledOptimizerTest.java

@@ -0,0 +1,113 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.id;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.SequenceGenerator;
+
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.dialect.DB2Dialect;
+import org.hibernate.dialect.PostgreSQLDialect;
+
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.JiraKey;
+import org.hibernate.testing.orm.junit.RequiresDialect;
+import org.hibernate.testing.orm.junit.RequiresDialects;
+import org.hibernate.testing.orm.junit.ServiceRegistry;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests sequence generation with pooled optimizer when using CTE-based batch inserts.
+ * Verifies that ID allocation works correctly across regular persists and batch operations.
+ *
+ * @author Kowsar Atazadeh
+ */
+@JiraKey("HHH-18818")
+@SessionFactory
+@RequiresDialects(
+		{
+				@RequiresDialect(PostgreSQLDialect.class),
+				@RequiresDialect(DB2Dialect.class),
+		}
+)
+@ServiceRegistry(
+		settings = {
+				@Setting(name = AvailableSettings.PREFERRED_POOLED_OPTIMIZER, value = "pooled"),
+		}
+)
+@DomainModel(annotatedClasses = { CteInsertStrategyWithPooledOptimizerTest.Dummy.class })
+public class CteInsertStrategyWithPooledOptimizerTest {
+	@Test
+	void test(SessionFactoryScope scope) {
+		// 9 rows inserted with IDs 1 to 9
+		// Two calls to the DB for next sequence value generation: first returns 6, second returns 11
+		// IDs 10 and 11 are still reserved for the PooledOptimizer
+		scope.inTransaction( session -> {
+			for ( var i = 1; i <= 9; i++ ) {
+				Dummy d = new Dummy( "d" + i );
+				session.persist( d );
+			}
+		} );
+
+		// 9 rows inserted (using CteInsertStrategy) with IDs 12 to 20 (before the fix, IDs would be 16 to 24)
+		// Two calls to the DB for next sequence value generation: first returns 16, second returns 21
+		scope.inTransaction( session -> {
+			session.createMutationQuery( "INSERT INTO Dummy (name) SELECT d.name FROM Dummy d" ).
+					executeUpdate();
+		} );
+
+		// Two rows inserted with the reserved IDs 10 and 11
+		scope.inTransaction( session -> {
+			session.persist( new Dummy( "d10" ) );
+			session.persist( new Dummy( "d11" ) );
+		} );
+
+		// One more row inserted with ID 22
+		// One call to the DB for next sequence value generation which returns 26 (IDs 22-26 allocated)
+		// Before the fix, this would result in a duplicate ID error (since batch insert used IDs 16 to 24)
+		scope.inTransaction( session -> {
+			session.persist( new Dummy( "d22" ) );
+		} );
+	}
+
+	@Entity(name = "Dummy")
+	static class Dummy {
+		@Id
+		@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "dummy_seq")
+		@SequenceGenerator(name = "dummy_seq", sequenceName = "dummy_seq", allocationSize = 5)
+		private Long id;
+
+		private String name;
+
+		public Dummy() {
+		}
+
+		public Dummy(String name) {
+			this.name = name;
+		}
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+}