[GitHub] [calcite-avatica] vaijosh commented on a diff in pull request #217: CALCITE-5581: Client side LB implementation

["vaijosh (via GitHub)" <gi...@apache.org>]

vaijosh commented on code in PR #217:
URL: https://github.com/apache/calcite-avatica/pull/217#discussion_r1144659331


##########
core/src/main/java/org/apache/calcite/avatica/ha/RoundRobinLBStrategy.java:
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@@ -0,0 +1,60 @@
+/*
+ * 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.calcite.avatica.ha;
+
+import org.apache.calcite.avatica.ConnectionConfig;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.regex.PatternSyntaxException;
+
+/**
+ * Round Robin strategy for client side load balancing.
+ * Its implemented it as a singleton so that we can maintain state
+ * i.e. which URL was last used from the list of URLs specified.
+ */
+public class RoundRobinLBStrategy implements LBStrategy {
+
+  public static final RoundRobinLBStrategy INSTANCE = new RoundRobinLBStrategy();
+  private RoundRobinLBStrategy() { }
+  public static final String URL_SEPERATOR_CHAR = ",";
+
+  Map<String, Integer>  configToIndexServedMap = new HashMap<>();

Review Comment:
   Config was natural choice. But from callers we don't always get same object (see AvaticaConnection.config). So this was not feasible. toString() method was another option I had considered, but it was a superset of config.getLbURLs().
   So config.getLbURLs() was a better option here.



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