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https://issues.apache.org/jira/browse/HBASE-30346?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Aman Poonia reassigned HBASE-30346:
-----------------------------------
Assignee: Aman Poonia
> NPE in AbstractFSWAL WAL-roll debug logging aborts RegionServer when
> DFSOutputStream#getPipeline() legitimately returns null
> ----------------------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-30346
> URL: https://issues.apache.org/jira/browse/HBASE-30346
> Project: HBase
> Issue Type: Bug
> Reporter: Aman Poonia
> Assignee: Aman Poonia
> Priority: Major
>
> *Symptom*
> RegionServers abort during WAL log rolling with:
>
> {{}}
> {code:java}
> java.lang.NullPointerException: Cannot read the array length because "array"
> is null at java.base/java.util.Arrays.stream(Arrays.java:5533) at
> org.apache.hadoop.hbase.regionserver.wal.AbstractFSWAL.rollWriterInternal(AbstractFSWAL.java:926)
> at
> org.apache.hadoop.hbase.regionserver.wal.AbstractFSWAL.rollWriter(AbstractFSWAL.java:...)
> at
> org.apache.hadoop.hbase.wal.AbstractWALRoller$RollController.rollWal(AbstractWALRoller.java:305)
> at
> org.apache.hadoop.hbase.wal.AbstractWALRoller.run(AbstractWALRoller.java:211)
>
> {code}
> followed by {{AbstractWALRoller}} catching the exception, logging {{{}"Log
> rolling failed"{}}}, and calling {{abort(...)}} on the RegionServer — a full
> RS self-abort, WAL splitting, and reassignment of every region the RS was
> carrying. Observed 9 times over a 68.8h window on a production cluster
> carrying 300–450+ regions per affected RS, driving the two longest
> region-in-transition episodes in that window.
> *Root cause*
> {{AbstractFSWAL.rollWriterInternal(boolean force)}} logs the newly-rolled
> WAL's DataNode pipeline for debugging, _after_ the roll has already succeeded
> ({{{}replaceWriter{}}} has already installed the new writer):
> if (LOG.isDebugEnabled()) \{
> LOG.debug("Create new " + implClassName + " writer with pipeline: "
> + FanOutOneBlockAsyncDFSOutputHelper
>
> .getDataNodeInfo(Arrays.stream(getPipeline()).collect(Collectors.toList())));
> }
> {{}}
> {{getPipeline()}} on the sync WAL path ({{{}FSHLog#getPipeline(){}}})
> delegates directly to Hadoop's {{{}DFSOutputStream#getPipeline(){}}}, which
> can legitimately return {{{}null{}}}:
> // returns the list of targets, if any, that is being currently used.
> @VisibleForTesting
> public synchronized DatanodeInfo[] getPipeline() \{
> if (getStreamer().streamerClosed()) {
> return null;
> }
> DatanodeInfo[] currentNodes = getStreamer().getNodes();
> if (currentNodes == null) \{
> return null;
> }
> ...
> }
> {{{}{}}}This is a documented, expected condition ("if any"), not an error:
> the underlying {{DataStreamer}} has no current pipeline before the first
> block is allocated, between blocks ({{{}DataStreamer#endBlock(){}}} resets
> {{nodes}} to {{{}null{}}}), or on a transient failed block-create retry.
> There is no non-null alternative accessor on
> {{{}DFSOutputStream{}}}/{{{}DataStreamer{}}}.
> {{Arrays.stream(null)}} throws NPE (unlike {{{}Arrays.toString(null){}}},
> which returns the string {{{}"null"{}}}). Because the debug-log statement
> sits inside a try block explicitly commented "Any exception from here on is
> catastrophic, non-recoverable, so we currently abort," the NPE is treated as
> a genuine roll failure and propagates to {{{}AbstractWALRoller{}}}, which
> aborts the RegionServer — even though the roll itself had already succeeded
> and only the diagnostic log line failed to format.
> *Regression*
> Introduced by HBASE-28775 ("Change the output of DatanodeInfo in the log to
> the hostname of the datanode", commit 53944cfc930a), which replaced the
> previously null-tolerant {{Arrays.toString(getPipeline())}} with the
> null-intolerant {{Arrays.stream(getPipeline()).collect(Collectors.toList())}}
> fed into {{{}FanOutOneBlockAsyncDFSOutputHelper#getDataNodeInfo{}}}.
> Confirmed present, unfixed, on {{master}} and {{{}branch-3{}}}.
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