Add a hibernate.default_batch_fetch_size value of 50

core/src/main/java/google/registry/config/RegistryConfig.java

@@ -1825,6 +1825,18 @@ public static String getHibernateJdbcFetchSize() {
     return CONFIG_SETTINGS.get().hibernate.jdbcFetchSize;
   }
 
+  /**
+   * Returns the Hibernate default batch fetch size ({@code hibernate.default_batch_fetch_size}).
+   *
+   * <p>This controls the maximum number of uninitialized child entities or collection proxies that
+   * Hibernate will batch together into a single {@code SELECT ... WHERE id IN (...)} query when
+   * loading / initializing child entities in the persistence context. This is not the standard
+   * "batch size" used when loading root entities in batches.
+   */
+  public static int getHibernateDefaultBatchFetchSize() {
+    return CONFIG_SETTINGS.get().hibernate.defaultBatchFetchSize;
+  }
+
   /** Returns the roid suffix to be used for the roids of all hosts. */
   public static String getHostRoidSuffix() {
     return CONFIG_SETTINGS.get().registryPolicy.contactAndHostRoidSuffix;

core/src/main/java/google/registry/config/RegistryConfigSettings.java

@@ -130,6 +130,7 @@ public static class Hibernate {
     public String hikariIdleTimeout;
     public int jdbcBatchSize;
     public String jdbcFetchSize;
+    public int defaultBatchFetchSize;
   }
 
   /** Configuration for Cloud SQL. */

core/src/main/java/google/registry/config/files/default-config.yaml

@@ -247,6 +247,12 @@ hibernate:
   # database cursor. Here we set a small default geared toward Nomulus server
   # transactions. Large queries can override the defaults on a per-query basis.
   jdbcFetchSize: 40
+  # The default batch fetch size is the maximum number of uninitialized child
+  # entities or collection proxies that Hibernate will load / initialize in a
+  # single batched SELECT query using an IN clause. This is not the same as the
+  # JDBC batch size, which controls batched insertions / updates of root
+  # entities.
+  defaultBatchFetchSize: 50
 
 cloudSql:
   # jdbc url for the Cloud SQL database.

core/src/main/java/google/registry/persistence/PersistenceModule.java

@@ -17,6 +17,7 @@
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static google.registry.config.RegistryConfig.getHibernateConnectionIsolation;
+import static google.registry.config.RegistryConfig.getHibernateDefaultBatchFetchSize;
 import static google.registry.config.RegistryConfig.getHibernateHikariConnectionTimeout;
 import static google.registry.config.RegistryConfig.getHibernateHikariIdleTimeout;
 import static google.registry.config.RegistryConfig.getHibernateHikariMaximumPoolSize;
@@ -84,6 +85,7 @@ public abstract class PersistenceModule {
 
   public static final String JDBC_BATCH_SIZE = "hibernate.jdbc.batch_size";
   public static final String JDBC_FETCH_SIZE = "hibernate.jdbc.fetch_size";
+  public static final String DEFAULT_BATCH_FETCH_SIZE = "hibernate.default_batch_fetch_size";
 
   @VisibleForTesting
   @Provides
@@ -113,6 +115,7 @@ public static ImmutableMap<String, String> provideDefaultDatabaseConfigs() {
     properties.put(Environment.DIALECT, NomulusPostgreSQLDialect.class.getName());
     properties.put(JDBC_BATCH_SIZE, Integer.toString(getHibernateJdbcBatchSize()));
     properties.put(JDBC_FETCH_SIZE, getHibernateJdbcFetchSize());
+    properties.put(DEFAULT_BATCH_FETCH_SIZE, Integer.toString(getHibernateDefaultBatchFetchSize()));
     return properties.build();
   }
 

core/src/test/java/google/registry/persistence/PersistenceModuleTest.java

@@ -15,7 +15,11 @@
 package google.registry.persistence;
 
 import static com.google.common.truth.Truth.assertThat;
+import static google.registry.persistence.PersistenceModule.DEFAULT_BATCH_FETCH_SIZE;
+import static google.registry.persistence.PersistenceModule.JDBC_BATCH_SIZE;
+import static google.registry.persistence.PersistenceModule.JDBC_FETCH_SIZE;
 
+import com.google.common.collect.ImmutableMap;
 import dagger.Component;
 import google.registry.config.CredentialModule;
 import google.registry.config.RegistryConfig.Config;
@@ -77,6 +81,14 @@ void connectionIsolation() {
         .isEqualTo(TransactionIsolationLevel.TRANSACTION_SERIALIZABLE.name());
   }
 
+  @Test
+  void batchAndFetchConfigs() {
+    ImmutableMap<String, String> configs = PersistenceModule.provideDefaultDatabaseConfigs();
+    assertThat(configs.get(JDBC_BATCH_SIZE)).isEqualTo("50");
+    assertThat(configs.get(JDBC_FETCH_SIZE)).isEqualTo("40");
+    assertThat(configs.get(DEFAULT_BATCH_FETCH_SIZE)).isEqualTo("50");
+  }
+
   @Singleton
   @Component(
       modules = {