[SENTRY-2299] NPE In Sentry HDFS Sync Plugin

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.1.0
• Fix Version/s: 2.2.0
• Component/s: Sentry
• Assignee: Na Li
• Reporter: Na Li
• Created: 06/Jul/18 20:23
• Updated: 02/Jan/20 17:07
• Resolved: 13/Jul/18 20:12

Description

Sentry HDFS ACL synchronization stopped working and throws NullPointerException. The HDFS logs showed repeating errors like the following:

11:16:15.743 AM	WARN	SentryAuthorizationInfo	
Failed to update, will retry in [30000]ms, error: 
java.lang.NullPointerException
at org.apache.sentry.hdfs.HMSPaths$Entry.access$200(HMSPaths.java:146)
at org.apache.sentry.hdfs.HMSPaths.renameAuthzObject(HMSPaths.java:879)
at org.apache.sentry.hdfs.UpdateableAuthzPaths.applyPartialUpdate(UpdateableAuthzPaths.java:118)
at org.apache.sentry.hdfs.UpdateableAuthzPaths.updatePartial(UpdateableAuthzPaths.java:81)
at org.apache.sentry.hdfs.SentryAuthorizationInfo.processUpdates(SentryAuthorizationInfo.java:211)
at org.apache.sentry.hdfs.SentryAuthorizationInfo.update(SentryAuthorizationInfo.java:139)
at org.apache.sentry.hdfs.SentryAuthorizationInfo.run(SentryAuthorizationInfo.java:232)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

The customer checked the Sentry logs and didn't see any corresponding errors. The issue stopped occurring, apparently not through any specific user intervention. (The customer tried manually failing over the active NameNode, with no change.)

Arjun mentioned the reason is that some delta update from sentry server was lost, so the oldEntry at line HMSPaths.java:879 was null. That caused null exception.

  void renameAuthzObject(String oldName, List<List<String>> oldPathElems,
      String newName, List<List<String>> newPathElems) {
    if (LOG.isDebugEnabled()) {
      LOG.debug(String.format("%s renameAuthzObject({%s, %s} -> {%s, %s})",
        this, oldName, assemblePaths(oldPathElems), newName, assemblePaths(newPathElems)));
    }
    if (oldPathElems == null || oldPathElems.isEmpty() ||
        newPathElems == null || newPathElems.isEmpty() ||
        newName == null || newName.equals(oldName)) {
      LOG.warn(String.format("%s renameAuthzObject({%s, %s} -> {%s, %s})" +
        ": invalid inputs, skipping",
        this, oldName, assemblePaths(oldPathElems), newName, assemblePaths(newPathElems)));
      return;
    }

    // if oldPath == newPath, that is path has not changed as part of rename and hence new table
    // needs to have old paths => new_table.add(old_table_partition_paths)
    List<String> oldPathElements = oldPathElems.get(0);
    List<String> newPathElements = newPathElems.get(0);
    if (!oldPathElements.equals(newPathElements)) {
      Entry oldEntry = root.find(oldPathElements.toArray(new String[0]), false);
      Entry newParent = root.createParent(newPathElements);
      oldEntry.moveTo(newParent, newPathElements.get(newPathElements.size() - 1)); -> oldEntry is null
    }

There are several possible reasons why some delta changes are lost.

1. Sentry server does not save the rename update as delta update. The chance is really low
2. The delta change is lost from sentry server to name node plugin. The chance is also low
3. When applying delta change about old entry, it is lost

The fix for this issue
1. Check if oldEntry is null. If so, don't call oldEntry.moveTo. Instead, throw exception, which will be caught by its caller and causes sentry client at name node plugin gets path full snapshot from sentry server.
2. Find out why the oldEntry is null and fix it.

Issue Links

• links to: Review Link for this case