Re: [PR] HDFS-17523: Add fine-grained lock held info when the lock holding time reaches the specified threshold [hadoop]

["slfan1989 (via GitHub)" <gi...@apache.org>]

slfan1989 commented on code in PR #6890:
URL: https://github.com/apache/hadoop/pull/6890#discussion_r1669463377


##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/AutoCloseDataSetLock.java:
##########
@@ -30,17 +33,39 @@
  * use a try-with-resource syntax.
  */
 public class AutoCloseDataSetLock extends AutoCloseableLock {
-  private Lock lock;
+
+  private final Lock lock;
+
+  private final DataNodeLockManager<AutoCloseDataSetLock> dataNodeLockManager;
+
+  private final boolean isReadLock;
+
+  private static ThreadLocal<DataSetLockHeldInfo> heldInfoThreadLocal = new

Review Comment:
   Sorry for the delayed response. I've been quite busy recently.
   Here's the detailed situation:
   
   In certain versions of JDK 17, there is an issue where weak references to ThreadLocal cannot be reclaimed(There is a problem with G1, but CMS can reclaim memory normally). This results in ThreadLocal objects accumulating a large amount of data, causing significant CPU overhead during traversal and element retrieval. We initially noticed this issue during latency profiling related to Ozone OM locks, where CPU usage for our OM spiked over a period of time. Hence, I suggested that enabling lock profiling should ideally be an optional feature.
   
   
   



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