Add a DelegatingReplicaJpaTransactionManager to handle multiple replicas (#3005)

This will allow us to spread the load across multiple Postgres replica
instances which should help with latency and stability.

core/src/test/java/google/registry/keyring/secretmanager/SecretManagerKeyringUpdaterTest.java

@@ -120,6 +120,23 @@ public class SecretManagerKeyringUpdaterTest {
     verifyPersistedSecret("sql-replica-conn-name", name);
   }
 
+  @Test
+  void sqlReplicaConnectionNames() {
+    String names = "name1\nname2";
+    updater.setSqlReplicaConnectionNames(names).update();
+
+    assertThat(keyring.getSqlReplicaConnectionNames()).containsExactly("name1", "name2").inOrder();
+    verifyPersistedSecret("sql-replica-conn-names", names);
+  }
+
+  @Test
+  void sqlReplicaConnectionNames_fallback() {
+    String name = "name";
+    updater.setSqlReplicaConnectionName(name).update();
+
+    assertThat(keyring.getSqlReplicaConnectionNames()).containsExactly(name);
+  }
+
   @Test
   void marksdbDnlLoginAndPassword() {
     String secret = "marksdbDnlLoginAndPassword";

core/src/test/java/google/registry/persistence/transaction/DelegatingReplicaJpaTransactionManagerTest.java

@@ -0,0 +1,135 @@
+// Copyright 2026 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.persistence.transaction;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import com.google.common.collect.ImmutableList;
+import java.util.Random;
+import java.util.concurrent.Callable;
+import org.junit.jupiter.api.Test;
+
+/** Tests for {@link DelegatingReplicaJpaTransactionManager}. */
+public class DelegatingReplicaJpaTransactionManagerTest {
+
+  private JpaTransactionManager replica1 = mock(JpaTransactionManager.class);
+  private JpaTransactionManager replica2 = mock(JpaTransactionManager.class);
+  private Random random = mock(Random.class);
+  private DelegatingReplicaJpaTransactionManager transactionManager =
+      new DelegatingReplicaJpaTransactionManager(ImmutableList.of(replica1, replica2), random);
+
+  @Test
+  void testGetReplica_rotates() {
+    when(random.nextInt(2)).thenReturn(0).thenReturn(1);
+
+    transactionManager.loadByKey(null);
+    verify(replica1).loadByKey(null);
+
+    transactionManager.loadByKey(null);
+    verify(replica2).loadByKey(null);
+  }
+
+  @Test
+  void testTransact_usesSameReplica() throws Exception {
+    when(random.nextInt(2)).thenReturn(1);
+    when(replica2.transact(any(), any(), anyBoolean()))
+        .thenAnswer(
+            invocation -> {
+              Callable<Object> work = invocation.getArgument(1);
+              return work.call();
+            });
+
+    transactionManager.transact(
+        () -> {
+          transactionManager.loadByKey(null);
+          return null;
+        });
+
+    verify(replica2).transact(any(), any(), anyBoolean());
+    // The loadByKey inside the transact should also use replica2.
+    verify(replica2).loadByKey(null);
+    // And it should NOT have called random again for the nested call.
+    verify(random).nextInt(2);
+  }
+
+  @Test
+  void testTransactNoRetry_usesSameReplica() throws Exception {
+    when(random.nextInt(2)).thenReturn(0);
+    when(replica1.transactNoRetry(any(), any(), anyBoolean()))
+        .thenAnswer(
+            invocation -> {
+              Callable<Object> work = invocation.getArgument(1);
+              return work.call();
+            });
+
+    transactionManager.transactNoRetry(
+        () -> {
+          transactionManager.loadByKey(null);
+          return null;
+        });
+
+    verify(replica1).transactNoRetry(any(), any(), anyBoolean());
+    verify(replica1).loadByKey(null);
+    verify(random).nextInt(2);
+  }
+
+  @Test
+  void testReTransactNoRetry_usesSameReplica() throws Exception {
+    when(random.nextInt(2)).thenReturn(0);
+    when(replica1.reTransact(any(Callable.class)))
+        .thenAnswer(
+            invocation -> {
+              Callable<Object> work = invocation.getArgument(0);
+              return work.call();
+            });
+
+    transactionManager.reTransact(
+        () -> {
+          transactionManager.loadByKey(null);
+          return null;
+        });
+
+    verify(replica1).reTransact(any(Callable.class));
+    verify(replica1).loadByKey(null);
+    verify(random).nextInt(2);
+  }
+
+  @Test
+  void testInTransaction() {
+    when(random.nextInt(2)).thenReturn(0);
+    when(replica1.inTransaction()).thenReturn(true);
+
+    // Not in transaction yet
+    assertThat(transactionManager.inTransaction()).isFalse();
+
+    transactionManager.transact(
+        () -> {
+          assertThat(transactionManager.inTransaction()).isTrue();
+          return null;
+        });
+  }
+
+  @Test
+  void testTeardown_tearsDownAllReplicas() {
+    transactionManager.teardown();
+    verify(replica1).teardown();
+    verify(replica2).teardown();
+  }
+}

core/src/test/java/google/registry/testing/FakeKeyringModule.java

@@ -19,6 +19,7 @@ import static google.registry.keyring.api.PgpHelper.KeyRequirement.SIGN;
 import static google.registry.testing.TestDataHelper.loadBytes;
 import static google.registry.testing.TestDataHelper.loadFile;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.io.ByteSource;
 import dagger.Module;
 import dagger.Provides;
@@ -57,7 +58,8 @@ public final class FakeKeyringModule {
   private static final String MARKSDB_SMDRL_LOGIN_AND_PASSWORD = "smdrl:yolo";
   private static final String BSA_API_KEY = "bsaapikey";
   private static final String SQL_PRIMARY_CONNECTION = "project:primary-region:primary-name";
-  private static final String SQL_REPLICA_CONNECTION = "project:replica-region:replica-name";
+  private static final String SQL_REPLICA_CONNECTION_1 = "project:replica-region:replica-name";
+  private static final String SQL_REPLICA_CONNECTION_2 = "project:replica-region:replica-name-2";
 
   @Provides
   public Keyring get() {
@@ -160,7 +162,12 @@ public final class FakeKeyringModule {
 
       @Override
       public String getSqlReplicaConnectionName() {
-        return SQL_REPLICA_CONNECTION;
+        return SQL_REPLICA_CONNECTION_1;
+      }
+
+      @Override
+      public ImmutableList<String> getSqlReplicaConnectionNames() {
+        return ImmutableList.of(SQL_REPLICA_CONNECTION_1, SQL_REPLICA_CONNECTION_2);
       }
 
       @Override