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From "Allan Yang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-18168) NoSuchElementException when rolling the log
Date Tue, 06 Jun 2017 08:49:18 GMT

     [ https://issues.apache.org/jira/browse/HBASE-18168?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Allan Yang updated HBASE-18168:
-------------------------------
    Status: Patch Available  (was: Open)

> NoSuchElementException when rolling the log
> -------------------------------------------
>
>                 Key: HBASE-18168
>                 URL: https://issues.apache.org/jira/browse/HBASE-18168
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.1.11
>            Reporter: Allan Yang
>            Assignee: Allan Yang
>         Attachments: HBASE-18168-branch-1.1.patch
>
>
> Today, one of our server aborted due to the following log.
> {code}
> 2017-06-06 05:38:47,142 ERROR [regionserver/xxxx.logRoller] regionserver.LogRoller: Log
rolling failed
> java.util.NoSuchElementException
>         at java.util.concurrent.ConcurrentSkipListMap$Iter.advance(ConcurrentSkipListMap.java:2224)
>         at java.util.concurrent.ConcurrentSkipListMap$ValueIterator.next(ConcurrentSkipListMap.java:2253)
>         at java.util.Collections.min(Collections.java:628)
>         at org.apache.hadoop.hbase.regionserver.wal.FSHLog.findEligibleMemstoresToFlush(FSHLog.java:861)
>         at org.apache.hadoop.hbase.regionserver.wal.FSHLog.findRegionsToForceFlush(FSHLog.java:886)
>         at org.apache.hadoop.hbase.regionserver.wal.FSHLog.rollWriter(FSHLog.java:728)
>         at org.apache.hadoop.hbase.regionserver.LogRoller.run(LogRoller.java:137)
>         at java.lang.Thread.run(Thread.java:756)
> 2017-06-06 05:38:47,142 FATAL [regionserver/xxxx.logRoller] regionserver.HRegionServer:
ABORTING region server xxxx: Log rolling failed
> java.util.NoSuchElementException
> ......
> {code}
> The code is here: 
> {code}
> private byte[][] findEligibleMemstoresToFlush(Map<byte[], Long> regionsSequenceNums)
{
>     List<byte[]> regionsToFlush = null;
>     // Keeping the old behavior of iterating unflushedSeqNums under oldestSeqNumsLock.
>     synchronized (regionSequenceIdLock) {
>       for (Map.Entry<byte[], Long> e: regionsSequenceNums.entrySet()) {
>         ConcurrentMap<byte[], Long> m =
>             this.oldestUnflushedStoreSequenceIds.get(e.getKey());
>         if (m == null) {
>           continue;
>         }
>         long unFlushedVal = Collections.min(m.values()); //The exception is thrown here
>         ......
> {code}
> The map 'm' is empty is the only reason I can think of why NoSuchElementException is
thrown. I then looked up all code related to the update of 'oldestUnflushedStoreSequenceIds'.
All update to 'oldestUnflushedStoreSequenceIds' is guarded by the synchronization of 'regionSequenceIdLock'
except here:
> {code}
> private ConcurrentMap<byte[], Long> getOrCreateOldestUnflushedStoreSequenceIdsOfRegion(
>       byte[] encodedRegionName) {
>     ......
>     oldestUnflushedStoreSequenceIdsOfRegion =
>         new ConcurrentSkipListMap<byte[], Long>(Bytes.BYTES_COMPARATOR);
>     ConcurrentMap<byte[], Long> alreadyPut =
>         oldestUnflushedStoreSequenceIds.putIfAbsent(encodedRegionName,
>           oldestUnflushedStoreSequenceIdsOfRegion); // Here, a empty map may put to 'oldestUnflushedStoreSequenceIds'
with no synchronization
>     return alreadyPut == null ? oldestUnflushedStoreSequenceIdsOfRegion : alreadyPut;
>   }
> {code}
> It should be a very rare bug. But it can lead to server abort. It only exists in branch-1.1.




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