NIFI-4773: Moved DB Fetch processors' connection code from setup to onTrigger

Signed-off-by: Pierre Villard <pierre.villard.fr@gmail.com>

This closes #2422.

nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/AbstractDatabaseFetchProcessor.java

@@ -50,6 +50,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.ServiceLoader;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import static java.sql.Types.ARRAY;
 import static java.sql.Types.BIGINT;
@@ -176,6 +177,10 @@ public abstract class AbstractDatabaseFetchProcessor extends AbstractSessionFact
     // pre-fetched when the processor is scheduled, rather than having to populate them on-the-fly.
     protected volatile boolean isDynamicMaxValues = false;
 
+    // This value is cleared when the processor is scheduled, and set to true after setup() is called and completes successfully. This enables
+    // the setup logic to be performed in onTrigger() versus OnScheduled to avoid any issues with DB connection when first scheduled to run.
+    protected final AtomicBoolean setupComplete = new AtomicBoolean(false);
+
     private static SimpleDateFormat TIME_TYPE_FORMAT = new SimpleDateFormat("HH:mm:ss.SSS");
 
     // A Map (name to value) of initial maximum-value properties, filled at schedule-time and used at trigger-time
@@ -222,11 +227,21 @@ public abstract class AbstractDatabaseFetchProcessor extends AbstractSessionFact
         return super.customValidate(validationContext);
     }
 
+    @Override
+    public void onPropertyModified(PropertyDescriptor descriptor, String oldValue, String newValue) {
+        // If the max-value columns have changed, we need to re-fetch the column info from the DB
+        if (MAX_VALUE_COLUMN_NAMES.equals(descriptor) && newValue != null && !newValue.equals(oldValue)) {
+            setupComplete.set(false);
+        }
+    }
+
     public void setup(final ProcessContext context) {
         setup(context,true,null);
     }
 
     public void setup(final ProcessContext context, boolean shouldCleanCache, FlowFile flowFile) {
+        synchronized (setupComplete) {
+            setupComplete.set(false);
             final String maxValueColumnNames = context.getProperty(MAX_VALUE_COLUMN_NAMES).evaluateAttributeExpressions(flowFile).getValue();
 
             // If there are no max-value column names specified, we don't need to perform this processing
@@ -266,6 +281,8 @@ public abstract class AbstractDatabaseFetchProcessor extends AbstractSessionFact
             } catch (SQLException e) {
                 throw new ProcessException("Unable to communicate with database in order to determine column types", e);
             }
+            setupComplete.set(true);
+        }
     }
 
     protected static String getMaxValueFromRow(ResultSet resultSet,

nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/GenerateTableFetch.java

@@ -155,9 +155,6 @@ public class GenerateTableFetch extends AbstractDatabaseFetchProcessor {
     @OnScheduled
     public void setup(final ProcessContext context) {
         maxValueProperties = getDefaultMaxValueProperties(context.getProperties());
-        if (!isDynamicTableName && !isDynamicMaxValues) {
-            super.setup(context);
-        }
         if (context.hasIncomingConnection() && !context.hasNonLoopConnection()) {
             getLogger().error("The failure relationship can be used only if there is another incoming connection to this processor.");
         }
@@ -165,6 +162,10 @@ public class GenerateTableFetch extends AbstractDatabaseFetchProcessor {
 
     @Override
     public void onTrigger(final ProcessContext context, final ProcessSessionFactory sessionFactory) throws ProcessException {
+        // Fetch the column/table info once (if the table name and max value columns are not dynamic). Otherwise do the setup later
+        if (!isDynamicTableName && !isDynamicMaxValues && !setupComplete.get()) {
+            super.setup(context);
+        }
         ProcessSession session = sessionFactory.createSession();
 
         FlowFile fileToProcess = null;

nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/QueryDatabaseTable.java

@@ -18,10 +18,10 @@ package org.apache.nifi.processors.standard;
 
 import org.apache.commons.lang3.StringUtils;
 import org.apache.nifi.annotation.behavior.DynamicProperty;
-import org.apache.nifi.annotation.behavior.EventDriven;
 import org.apache.nifi.annotation.behavior.InputRequirement;
 import org.apache.nifi.annotation.behavior.InputRequirement.Requirement;
 import org.apache.nifi.annotation.behavior.Stateful;
+import org.apache.nifi.annotation.behavior.TriggerSerially;
 import org.apache.nifi.annotation.behavior.WritesAttribute;
 import org.apache.nifi.annotation.behavior.WritesAttributes;
 import org.apache.nifi.annotation.documentation.CapabilityDescription;
@@ -73,7 +73,7 @@ import static org.apache.nifi.processors.standard.util.JdbcCommon.NORMALIZE_NAME
 import static org.apache.nifi.processors.standard.util.JdbcCommon.USE_AVRO_LOGICAL_TYPES;
 
 
-@EventDriven
+@TriggerSerially
 @InputRequirement(Requirement.INPUT_FORBIDDEN)
 @Tags({"sql", "select", "jdbc", "query", "database"})
 @SeeAlso({GenerateTableFetch.class, ExecuteSQL.class})
@@ -178,11 +178,14 @@ public class QueryDatabaseTable extends AbstractDatabaseFetchProcessor {
     @OnScheduled
     public void setup(final ProcessContext context) {
         maxValueProperties = getDefaultMaxValueProperties(context.getProperties());
-        super.setup(context);
     }
 
     @Override
     public void onTrigger(final ProcessContext context, final ProcessSessionFactory sessionFactory) throws ProcessException {
+        // Fetch the column/table info once
+        if (!setupComplete.get()) {
+            super.setup(context);
+        }
         ProcessSession session = sessionFactory.createSession();
         final List<FlowFile> resultSetFlowFiles = new ArrayList<>();