Make read-only transactions more performant (#2233)

Since the replica SQL instance is read-only, any transaction performed
on it should be explicitly read-only, which would allow PostgreSQL to
optimize away (some) use of predicate locks.

Also changed the EPP cache to read from the replica. The foreign key
cache already behaves this way.

See: https://www.postgresql.org/docs/current/transaction-iso.html

core/src/main/java/google/registry/model/EppResource.java

@@ -20,6 +20,7 @@ import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.union;
 import static google.registry.config.RegistryConfig.getEppResourceCachingDuration;
 import static google.registry.config.RegistryConfig.getEppResourceMaxCachedEntries;
+import static google.registry.persistence.transaction.TransactionManagerFactory.replicaTm;
 import static google.registry.persistence.transaction.TransactionManagerFactory.tm;
 import static google.registry.util.CollectionUtils.nullToEmpty;
 import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
@@ -357,13 +358,13 @@ public abstract class EppResource extends UpdateAutoTimestampEntity implements B
 
         @Override
         public EppResource load(VKey<? extends EppResource> key) {
-          return tm().reTransact(() -> tm().loadByKey(key));
+          return replicaTm().reTransact(() -> replicaTm().loadByKey(key));
         }
 
         @Override
         public Map<VKey<? extends EppResource>, EppResource> loadAll(
             Iterable<? extends VKey<? extends EppResource>> keys) {
-          return tm().reTransact(() -> tm().loadByKeys(keys));
+          return replicaTm().reTransact(() -> replicaTm().loadByKeys(keys));
         }
       };
 

core/src/main/java/google/registry/model/ForeignKeyUtils.java

@@ -165,10 +165,11 @@ public final class ForeignKeyUtils {
    * foreign keys should not use this cache.
    *
    * <p>Note that here the key of the {@link LoadingCache} is of type {@code VKey<? extends
-   * EppResource>}, but they are not legal {VKey}s to {@link EppResource}s, whose keys are the SQL
-   * primary keys, i.e. the {@code repoId}s. Instead, their keys are the foreign keys used to query
-   * the database. We use {@link VKey} here because it is a convenient composite class that contains
-   * both the resource type and the foreign key, which are needed to for the query and caching.
+   * EppResource>}, but they are not legal {@link VKey}s to {@link EppResource}s, whose keys are the
+   * SQL primary keys, i.e. the {@code repoId}s. Instead, their keys are the foreign keys used to
+   * query the database. We use {@link VKey} here because it is a convenient composite class that
+   * contains both the resource type and the foreign key, which are needed to for the query and
+   * caching.
    *
    * <p>Also note that the value type of this cache is {@link Optional} because the foreign keys in
    * question are coming from external commands, and thus don't necessarily represent entities in

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

@@ -267,7 +267,7 @@ public abstract class PersistenceModule {
         name -> overrides.put(HIKARI_DS_CLOUD_SQL_INSTANCE, name));
     overrides.put(
         Environment.ISOLATION, TransactionIsolationLevel.TRANSACTION_REPEATABLE_READ.name());
-    return new JpaTransactionManagerImpl(create(overrides), clock);
+    return new JpaTransactionManagerImpl(create(overrides), clock, true);
   }
 
   @Provides
@@ -283,7 +283,7 @@ public abstract class PersistenceModule {
         name -> overrides.put(HIKARI_DS_CLOUD_SQL_INSTANCE, name));
     overrides.put(
         Environment.ISOLATION, TransactionIsolationLevel.TRANSACTION_REPEATABLE_READ.name());
-    return new JpaTransactionManagerImpl(create(overrides), clock);
+    return new JpaTransactionManagerImpl(create(overrides), clock, true);
   }
 
   /** Constructs the {@link EntityManagerFactory} instance. */

core/src/main/java/google/registry/persistence/transaction/JpaTransactionManagerImpl.java

@@ -85,13 +85,19 @@ public class JpaTransactionManagerImpl implements JpaTransactionManager {
   // EntityManagerFactory is thread safe.
   private final EntityManagerFactory emf;
   private final Clock clock;
+  private final boolean readOnly;
 
   private static final ThreadLocal<TransactionInfo> transactionInfo =
       ThreadLocal.withInitial(TransactionInfo::new);
 
-  public JpaTransactionManagerImpl(EntityManagerFactory emf, Clock clock) {
+  public JpaTransactionManagerImpl(EntityManagerFactory emf, Clock clock, boolean readOnly) {
     this.emf = emf;
     this.clock = clock;
+    this.readOnly = readOnly;
+  }
+
+  public JpaTransactionManagerImpl(EntityManagerFactory emf, Clock clock) {
+    this(emf, clock, false);
   }
 
   @Override
@@ -200,6 +206,10 @@ public class JpaTransactionManagerImpl implements JpaTransactionManager {
     try {
       txn.begin();
       txnInfo.start(clock);
+      if (readOnly) {
+        getEntityManager().createNativeQuery("SET TRANSACTION READ ONLY").executeUpdate();
+        logger.atInfo().log("Using read-only SQL replica");
+      }
       if (isolationLevel != null && isolationLevel != getDefaultTransactionIsolationLevel()) {
         getEntityManager()
             .createNativeQuery(