HADOOP-18138. UserGroupInformation shouldn't log exception unnecessarily

[sunchao]

Description of PR

In UserGroupInformation.doAs, we currently create a new Exception and log it in LOG.debug. This doesn't look necessary:

      if (LOG.isDebugEnabled()) {
        LOG.debug("PrivilegedAction [as: {}][action: {}]", this, action,
            new Exception());
      }

How was this patch tested?

Existing tests.

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

💔 -1 overall

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-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	34m 51s		trunk passed
+1 💚	compile	24m 9s		trunk passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	compile	20m 42s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	0m 59s		trunk passed
+1 💚	mvnsite	1m 36s		trunk passed
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+1 💚	javadoc	1m 38s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	2m 31s		trunk passed
+1 💚	shadedclient	25m 1s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 2s		the patch passed
+1 💚	compile	23m 31s		the patch passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	javac	23m 31s		the patch passed
+1 💚	compile	20m 50s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	20m 50s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	1m 2s		the patch passed
+1 💚	mvnsite	1m 36s		the patch passed
+1 💚	javadoc	1m 5s		the patch passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	javadoc	1m 40s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	2m 39s		the patch passed
+1 💚	shadedclient	25m 28s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	28m 16s		hadoop-common in the patch passed.
+1 💚	asflicense	0m 49s		The patch does not generate ASF License warnings.
		221m 11s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4007/1/artifact/out/Dockerfile
GITHUB PR	#4007
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
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git revision	trunk / c463cd0
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modules	C: hadoop-common-project/hadoop-common U: hadoop-common-project/hadoop-common
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[jojochuang]

I thought it was intentional, to log the stack trace of where it was being called?

[sunchao]

I see. Didn't know the context. It's a bit confusing to see the stack trace like this though:

PrivilegedAction [as: <principal> (auth:KERBEROS)][action: org.apache.hadoop.ipc.Client$Connection$2@65fa2f2d]
java.lang.Exception: null
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1875) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:838) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.Client$Connection.access$3800(Client.java:414) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.Client.getConnection(Client.java:1654) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.Client.call(Client.java:1479) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.Client.call(Client.java:1432) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.ProtobufRpcEngine2$Invoker.invoke(ProtobufRpcEngine2.java:242) ~[hadoop-client-api-3.3.1.jar:?]
	at org.apache.hadoop.ipc.ProtobufRpcEngine2$Invoker.invoke(ProtobufRpcEngine2.java:129) ~[hadoop-client-api-3.3.1.jar:?]
	at com.sun.proxy.$Proxy14.delete(Unknown Source) ~[?:?]

and it could makes people think there's something wrong in the doAs method. Maybe we can strip the first line of the stacktrace and replace with something like:

PrivilegedAction [as: <principal> (auth:KERBEROS)][action: org.apache.hadoop.ipc.Client$Connection$2@65fa2f2d]
Call stacktrace:
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1875) ~[hadoop-client-api-3.3.1.jar:?]

[busbey]

I'm wary of things that require us to reimplement the logging system handling the stack trace details. Maybe we could convey the purpose in either the exception message or the exception type instead?

e.g.

      if (LOG.isDebugEnabled()) {
        LOG.debug("PrivilegedAction [as: {}][action: {}]", this, action,
            new JustForDebuggingException("call stack for privileged action; not an indication of a failure"));
      }