CAY-2954 Do not wrap selecting queries in transactions

Author: andrus

RELEASE-NOTES.txt

@@ -13,6 +13,7 @@ Date:
 ----------------------------------
 Changes/New Features:
 
+CAY-2954 Don't wrap selecting queries in transactions
 CAY-2956 Get rid of a dedicated adapter for Oracle 8
 CAY-2957 Get rid of adapter for legacy HSQLDB <= 1.8
 CAY-2963 Replace TypesHandler / types.xml with hardcoded map

cayenne/src/main/java/org/apache/cayenne/access/DataDomainQueryAction.java

@@ -54,6 +54,7 @@
 import org.apache.cayenne.reflect.ClassDescriptor;
 import org.apache.cayenne.reflect.LifecycleCallbackRegistry;
 import org.apache.cayenne.tx.BaseTransaction;
+import org.apache.cayenne.tx.ReadOnlyTransaction;
 import org.apache.cayenne.tx.Transaction;
 import org.apache.cayenne.util.GenericResponse;
 import org.apache.cayenne.util.ListResponse;
@@ -483,10 +484,17 @@ private QueryCacheEntryFactory getCacheObjectFactory() {
      * Gets response from the underlying DataNodes.
      */
     void runQueryInTransaction() {
-        domain.getTransactionManager().performInTransaction(() -> {
-            runQuery();
-            return null;
-        });
+        if (metadata.isReadOnly() && BaseTransaction.getThreadTransaction() == null) {
+            domain.getTransactionManager().performInTransaction(() -> {
+                runQuery();
+                return null;
+            }, descriptor -> new ReadOnlyTransaction());
+        } else {
+            domain.getTransactionManager().performInTransaction(() -> {
+                runQuery();
+                return null;
+            });
+        }
     }
 
     private void runQuery() {

cayenne/src/main/java/org/apache/cayenne/access/DataNodeQueryAction.java

@@ -19,20 +19,19 @@
 
 package org.apache.cayenne.access;
 
-import java.sql.Connection;
-import java.sql.SQLException;
-import java.util.List;
-
 import org.apache.cayenne.ObjectId;
 import org.apache.cayenne.ResultIterator;
 import org.apache.cayenne.query.Query;
 import org.apache.cayenne.query.SQLAction;
 
+import java.sql.Connection;
+import java.util.List;
+
 /**
  * A helper that executes a sequence of queries, providing correct mapping of the results
  * to the original query. Note that this class is not thread-safe as it stores current
  * query execution state.
- * 
+ *
  * @since 1.2
  */
 class DataNodeQueryAction {
@@ -45,8 +44,7 @@ public DataNodeQueryAction(DataNode node, OperationObserver observer) {
         this.node = node;
     }
 
-    public void runQuery(Connection connection, final Query originalQuery)
-            throws SQLException, Exception {
+    public void runQuery(Connection connection, Query originalQuery) throws Exception {
 
         // wrap to ensure that the result is mapped back to the original query, even if
         // the underlying SQLAction uses query substitute...
@@ -71,7 +69,7 @@ public void nextRows(Query query, List<?> dataRows) {
             public void nextRows(Query q, ResultIterator it) {
                 observer.nextRows(originalQuery, it);
             }
-            
+
             @Override
             public void nextGeneratedRows(Query query, ResultIterator<?> keys, List<ObjectId> idsToUpdate) {
                 observer.nextGeneratedRows(originalQuery, keys, idsToUpdate);

cayenne/src/main/java/org/apache/cayenne/access/jdbc/SelectAction.java

@@ -75,12 +75,15 @@ public SelectAction(Select<?> query, DataNode dataNode) {
 
     @Override
     public void performAction(Connection connection, OperationObserver observer) throws Exception {
+        TranslatedSelect translated = dataNode.getSelectTranslator().translate(query, dataNode.getAdapter(), dataNode.getEntityResolver());
+        performAction(connection, observer, translated);
+    }
+
+    protected void performAction(Connection connection, OperationObserver observer, TranslatedSelect translated) throws Exception {
 
         long t1 = System.currentTimeMillis();
 
         JdbcEventLogger logger = dataNode.getJdbcEventLogger();
-        TranslatedSelect translated = dataNode.getSelectTranslator()
-                .translate(query, dataNode.getAdapter(), dataNode.getEntityResolver());
 
         logger.logQuery(translated.sql(), translated.bindings());
 

cayenne/src/main/java/org/apache/cayenne/dba/AutoAdapter.java

@@ -152,6 +152,7 @@ public boolean supportsGeneratedKeysForBatchInserts() {
 		return getAdapter().supportsGeneratedKeysForBatchInserts();
 	}
 
+
 	@Override
 	public boolean supportsBatchUpdates() {
 		return getAdapter().supportsBatchUpdates();

cayenne/src/main/java/org/apache/cayenne/dba/postgres/PostgresSelectAction.java

@@ -19,9 +19,17 @@
 package org.apache.cayenne.dba.postgres;
 
 import org.apache.cayenne.access.DataNode;
+import org.apache.cayenne.access.OperationObserver;
+import org.apache.cayenne.access.jdbc.ColumnDescriptor;
 import org.apache.cayenne.access.jdbc.SelectAction;
+import org.apache.cayenne.access.translator.ParameterBinding;
+import org.apache.cayenne.access.translator.select.TranslatedSelect;
 import org.apache.cayenne.query.Select;
 
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Types;
+
 /**
  * @since 3.0
  */
@@ -35,4 +43,52 @@ <T> PostgresSelectAction(Select<T> query, DataNode dataNode) {
 	protected int getInMemoryOffset(int queryOffset) {
 		return 0;
 	}
+
+	@Override
+	protected void performAction(Connection connection, OperationObserver observer, TranslatedSelect translated) throws Exception {
+
+		if (!connection.getAutoCommit() || !readsLargeObjects(translated)) {
+			super.performAction(connection, observer, translated);
+			return;
+		}
+
+		// manual tx management for reading LOBs
+		connection.setAutoCommit(false);
+		try {
+			super.performAction(connection, observer, translated);
+			connection.commit();
+		} catch (Exception e) {
+			try {
+				connection.rollback();
+			} catch (SQLException ignored) {
+				// connection is being returned/closed anyway
+			}
+			throw e;
+		} finally {
+			try {
+				connection.setAutoCommit(true);
+			} catch (SQLException ignored) {
+				// connection is being returned/closed anyway
+			}
+		}
+	}
+
+	private static boolean readsLargeObjects(TranslatedSelect translated) {
+		for (ColumnDescriptor column : translated.resultColumns()) {
+			if (isLargeObject(column.getJdbcType())) {
+				return true;
+			}
+		}
+		// a large object bound as a parameter (e.g. in a qualifier) also needs a transaction
+		for (ParameterBinding binding : translated.bindings()) {
+			if (isLargeObject(binding.getJdbcType())) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private static boolean isLargeObject(int jdbcType) {
+		return jdbcType == Types.BLOB || jdbcType == Types.CLOB || jdbcType == Types.NCLOB;
+	}
 }

cayenne/src/main/java/org/apache/cayenne/query/ObjectIdQuery.java

@@ -105,6 +105,11 @@ public ObjEntity getObjEntity() {
                 public boolean isFetchingDataRows() {
                     return fetchingDataRows;
                 }
+
+                @Override
+                public boolean isReadOnly() {
+                    return true;
+                }
             };
 
             this.metadataResolver = resolver;

cayenne/src/main/java/org/apache/cayenne/query/ObjectSelectMetadata.java

@@ -39,6 +39,14 @@ class ObjectSelectMetadata extends BaseQueryMetadata {
 
 	protected Map<String, String> pathSplitAliases;
 
+	/**
+	 * @since 5.0
+	 */
+	@Override
+	public boolean isReadOnly() {
+		return true;
+	}
+
 	@Override
 	void copyFromInfo(QueryMetadata info) {
 		super.copyFromInfo(info);

cayenne/src/main/java/org/apache/cayenne/query/QueryMetadata.java

@@ -264,4 +264,15 @@ default void setResultSetMapping(List<Object> resultSetMapping) {
     default Function<?, ?> getResultMapper() {
         return null;
     }
+
+    /**
+     * Returns true if this is a read-only (selecting) query that does not need to run in its own
+     * transaction. Defaults to false, so any query not explicitly marked read-only is still wrapped
+     * in a transaction.
+     *
+     * @since 5.0
+     */
+    default boolean isReadOnly() {
+        return false;
+    }
 }

cayenne/src/main/java/org/apache/cayenne/query/QueryMetadataProxy.java

@@ -141,4 +141,9 @@ public int getQueryTimeout() {
     public boolean isSuppressingDistinct() {
         return mdDelegate.isSuppressingDistinct();
     }
+
+    @Override
+    public boolean isReadOnly() {
+        return mdDelegate.isReadOnly();
+    }
 }