Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/956#discussion_r13477209
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala ---
@@ -0,0 +1,71 @@
+/*
+ * 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.spark.sql
+
+import java.util.Properties
+
+import scala.collection.mutable
+
+/**
+ * SQLConf holds mutable config parameters and hints. These can be set and
+ * queried either by passing SET commands into Spark SQL's DSL
+ * functions (sql(), hql(), etc.), or by programmatically using setters and
+ * getters of this class.
+ */
+class SQLConf {
+
+ protected val settings = new mutable.HashMap[String, String]()
--- End diff --
I meant java.util.Collections.synchronizedMap
Don't use ConcurrentHashMap - it has terrible memory footprint and
performance in low contention. In most cases, this will be accessed in a single
thread.
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