dbwong commented on code in PR #1430:
URL: https://github.com/apache/phoenix/pull/1430#discussion_r898677379


##########
phoenix-core/src/main/java/org/apache/phoenix/jdbc/HighAvailabilityPolicy.java:
##########
@@ -0,0 +1,141 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.phoenix.jdbc;
+
+import static org.apache.phoenix.jdbc.ClusterRoleRecord.ClusterRole.ACTIVE;
+import static org.apache.phoenix.jdbc.ClusterRoleRecord.ClusterRole.STANDBY;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.List;
+import java.util.Properties;
+
+import org.apache.phoenix.exception.SQLExceptionCode;
+import org.apache.phoenix.exception.SQLExceptionInfo;
+import org.apache.phoenix.monitoring.GlobalClientMetrics;
+import org.apache.phoenix.query.ConnectionQueryServices;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * An HighAvailabilityGroup provides a JDBC connection from given connection 
string and properties.
+ */
+enum HighAvailabilityPolicy {
+    FAILOVER {
+        @Override
+        public Connection provide(HighAvailabilityGroup haGroup, Properties 
info)
+                throws SQLException {
+            return new FailoverPhoenixConnection(haGroup, info);
+        }
+        @Override
+        void transitClusterRole(HighAvailabilityGroup haGroup, 
ClusterRoleRecord oldRecord,
+                ClusterRoleRecord newRecord) throws SQLException {
+            if (oldRecord.getRole1() == ACTIVE && newRecord.getRole1() == 
STANDBY) {
+                transitStandby(haGroup, oldRecord.getZk1());
+            }
+            if (oldRecord.getRole2() == ACTIVE && newRecord.getRole2() == 
STANDBY) {
+                transitStandby(haGroup, oldRecord.getZk2());
+            }
+            if (oldRecord.getRole1() != ACTIVE && newRecord.getRole1() == 
ACTIVE) {
+                transitActive(haGroup, oldRecord.getZk1());
+            }
+            if (oldRecord.getRole2() != ACTIVE && newRecord.getRole2() == 
ACTIVE) {
+                transitActive(haGroup, oldRecord.getZk2());
+            }
+        }
+        private void transitStandby(HighAvailabilityGroup haGroup, String 
zkUrl)
+                throws SQLException {
+            // Close connections when a previously ACTIVE HBase cluster 
becomes STANDBY.
+            LOG.info("Cluster {} becomes STANDBY in HA group {}, now close all 
its connections",
+                    zkUrl, haGroup.getGroupInfo());
+            ConnectionQueryServices cqs = null;
+            try {
+                cqs = PhoenixDriver.INSTANCE.getConnectionQueryServices(zkUrl,
+                         haGroup.getProperties());
+                cqs.closeAllConnections(new SQLExceptionInfo
+                        .Builder(SQLExceptionCode.HA_CLOSED_AFTER_FAILOVER)
+                        .setMessage("Phoenix connection got closed due to 
failover")
+                        .setHaGroupInfo(haGroup.getGroupInfo().toString()));
+                LOG.info("Closed all connections to cluster {} for HA group 
{}", zkUrl,
+                        haGroup.getGroupInfo());
+            } finally {
+                if (cqs != null) {
+                    // CQS is closed but it is not invalidated from global 
cache in PhoenixDriver
+                    // so that any new connection will get error instead of 
creating a new CQS
+                    LOG.info("Closing CQS after cluster '{}' becomes STANDBY", 
zkUrl);
+                    cqs.close();
+                    LOG.info("Successfully closed CQS after cluster '{}' 
becomes STANDBY", zkUrl);
+                }
+            }
+        }
+        private void transitActive(HighAvailabilityGroup haGroup, String zkUrl)
+                throws SQLException {
+            // Invalidate CQS cache if any that has been closed but has not 
been cleared
+            PhoenixDriver.INSTANCE.invalidateCache(zkUrl, 
haGroup.getProperties());
+        }
+    },
+
+    PARALLEL {
+        @Override
+        public Connection provide(HighAvailabilityGroup haGroup, Properties 
info)
+                throws SQLException {
+            List<Boolean> executorCapacities = 
PhoenixHAExecutorServiceProvider.hasCapacity(info);
+            if (executorCapacities.contains(Boolean.TRUE)) {
+                ParallelPhoenixContext context =
+                        new ParallelPhoenixContext(info, haGroup,
+                                PhoenixHAExecutorServiceProvider.get(info), 
executorCapacities);
+                return new ParallelPhoenixConnection(context);
+            } else {
+                // TODO: Once we have operation/primary wait timeout use the 
same
+                // Give regular connection or a failover connection?
+                LOG.warn("Falling back to single phoenix connection due to 
resource constraints");
+                
GlobalClientMetrics.GLOBAL_HA_PARALLEL_CONNECTION_FALLBACK_COUNTER.increment();
+                return haGroup.connectActive(info);
+            }
+        }
+        @Override
+        void transitClusterRole(HighAvailabilityGroup haGroup, 
ClusterRoleRecord oldRecord,
+                ClusterRoleRecord newRecord) {
+            LOG.info("Cluster role changed for parallel HA policy.");

Review Comment:
   We don't expect anything to change so it would be good to have a log that 
something tried to change it.  Parallel does not differentiate between any 
state.



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