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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3889) NPE in Distributed Log Splitting
Date Tue, 14 Jun 2011 20:42:47 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3889?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13049398#comment-13049398
] 

stack commented on HBASE-3889:
------------------------------

@Anirudh Test looks good.  Do you want to include in your patch Lars fix or you want me to
apply that separate?  Do you want to redo it addressing issues raised by Prakash (while considering
Lars' follow up?)

> NPE in Distributed Log Splitting
> --------------------------------
>
>                 Key: HBASE-3889
>                 URL: https://issues.apache.org/jira/browse/HBASE-3889
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.92.0
>         Environment: Pseudo-distributed on MacOS
>            Reporter: Lars George
>            Assignee: stack
>            Priority: Blocker
>             Fix For: 0.92.0
>
>         Attachments: HBASE-3889.patch, patch.txt
>
>
> There is an issue with the log splitting under the specific condition of edits belonging
to a non existing region (which went away after a split for example). The HLogSplitter fails
to check the condition, which is handled on a lower level, logging manifests it as 
> {noformat}
> 2011-05-16 13:56:10,300 INFO org.apache.hadoop.hbase.regionserver.wal.HLogSplitter: This
region's directory doesn't exist: hdfs://localhost:8020/hbase/usertable/30c4d0a47703214845d0676d0c7b36f0.
It is very likely that it was already split so it's safe to discard those edits.
> {noformat}
> The code returns a null reference which is not check in HLogSplitter.splitLogFileToTemp():
> {code}
> ...
>         WriterAndPath wap = (WriterAndPath)o;
>         if (wap == null) {
>           wap = createWAP(region, entry, rootDir, tmpname, fs, conf);
>           if (wap == null) {
>             logWriters.put(region, BAD_WRITER);
>           } else {
>             logWriters.put(region, wap);
>           }
>         }
>         wap.w.append(entry);
> ...
> {code}
> The createWAP does return "null" when the above message is logged based on the obsolete
region reference in the edit.
> What made this difficult to detect is that the error (and others) are silently ignored
in SplitLogWorker.grabTask(). I added a catch and error logging to see the NPE that was caused
by the above.
> {code}
> ...
>           break;
>       }
>     } catch (Exception e) {
>       LOG.error("An error occurred.", e);
>     } finally {
>       if (t > 0) {
> ...
> {code}
> As a side note, there are other errors/asserts triggered that this try/finally not handles.
For example
> {noformat}
> 2011-05-16 13:58:30,647 WARN org.apache.hadoop.hbase.regionserver.SplitLogWorker: BADVERSION
failed to assert ownership for /hbase/splitlog/hdfs%3A%2F%2Flocalhost%2Fhbase%2F.logs%2F10.0.0.65%2C60020%2C1305406356765%2F10.0.0.65%252C60020%252C1305406356765.1305409968389
> org.apache.zookeeper.KeeperException$BadVersionException: KeeperErrorCode = BadVersion
for /hbase/splitlog/hdfs%3A%2F%2Flocalhost%2Fhbase%2F.logs%2F10.0.0.65%2C60020%2C1305406356765%2F10.0.0.65%252C60020%252C1305406356765.1305409968389
>         at org.apache.zookeeper.KeeperException.create(KeeperException.java:106)
>         at org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
>         at org.apache.zookeeper.ZooKeeper.setData(ZooKeeper.java:1038)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker.ownTask(SplitLogWorker.java:329)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker.access$100(SplitLogWorker.java:68)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker$2.progress(SplitLogWorker.java:265)
>         at org.apache.hadoop.hbase.regionserver.wal.HLogSplitter.splitLogFileToTemp(HLogSplitter.java:432)
>         at org.apache.hadoop.hbase.regionserver.wal.HLogSplitter.splitLogFileToTemp(HLogSplitter.java:354)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker$1.exec(SplitLogWorker.java:113)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker.grabTask(SplitLogWorker.java:260)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker.taskLoop(SplitLogWorker.java:191)
>         at org.apache.hadoop.hbase.regionserver.SplitLogWorker.run(SplitLogWorker.java:164)
>         at java.lang.Thread.run(Thread.java:680)
> {noformat}
> This should probably be handled - or at least documented - in another issue?
> The NPE made the log split end and the SplitLogManager add an endless amount of RESCAN
entries as this never came to an end.

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