Github user aarondav commented on a diff in the pull request:
https://github.com/apache/spark/pull/1272#discussion_r14407762
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala ---
@@ -50,8 +50,7 @@ trait SQLConf {
/** ********************** SQLConf functionality methods ************ */
@transient
- private val settings = java.util.Collections.synchronizedMap(
- new java.util.HashMap[String, String]())
+ private val settings = new
java.util.concurrent.ConcurrentHashMap[String, String]()
--- End diff --
@rxin I think the performance distinction is extremely minor in this case,
as there is only one ConcurrentHashMap. ConcurrentHashMap's API tends to be
nicer to use, though, as people may not realize that iteration over a
SynchronizedMap is not threadsafe, like in the current implementation of
SQLConf.
As @baishuo mentioned, if we use synchronizedMap we'll have to add
settings.synchronized {} in a few places now.
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