[SQL] add note of use synchronizedMap in SQLConf

Refer to: http://stackoverflow.com/questions/510632/whats-the-difference-between-concurrenthashmap-and-collections-synchronizedmap Collections.synchronizedMap(map) creates a blocking Map which will degrade performance, albeit ensure consistency. So use ConcurrentHashMap(a more effective thread-safe hashmap) instead. also update HiveQuerySuite to fix test error when changed to ConcurrentHashMap. Author: wangfei <[email protected]> Author: scwf <[email protected]> Closes apache#1996 from scwf/sqlconf and squashes the following commits: 93bc0c5 [wangfei] revert change of HiveQuerySuite 0cc05dd [wangfei] add note for use synchronizedMap 3c224d3 [scwf] fix formate a7bcb98 [scwf] use ConcurrentHashMap in sql conf, intead synchronizedMap
xiliu82 · Sep 4, 2014 · 674c9ab · 674c9ab
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commit 674c9ab
Showing 1 changed file with 1 addition and 0 deletions.
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala b/sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala
@@ -54,6 +54,7 @@ private[spark] object SQLConf {
 trait SQLConf {
   import SQLConf._
 
+  /** Only low degree of contention is expected for conf, thus NOT using ConcurrentHashMap. */
   @transient protected[spark] val settings = java.util.Collections.synchronizedMap(
     new java.util.HashMap[String, String]())