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https://issues.apache.org/jira/browse/ACCUMULO-942?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eric Newton resolved ACCUMULO-942.
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Resolution: Won't Fix
See ACCUMULO-919
> accumulo should be more resilient in the face of NN failures
> ------------------------------------------------------------
>
> Key: ACCUMULO-942
> URL: https://issues.apache.org/jira/browse/ACCUMULO-942
> Project: Accumulo
> Issue Type: Bug
> Components: tserver
> Reporter: Eric Newton
> Assignee: Eric Newton
> Priority: Critical
>
> We experienced a NN failure on a large cluster. The edit log was written to
> a RAIDed file system, but it did lose data sent to the edit log. We suspect
> drivers making promises it did not keep.
> This left Accumulo in a slightly corrupt state: a few references to files
> that were missing.
> Also, we have attempted to have backup images of HDFS archived for disaster
> recovery. This has not been helpful because Accumulo needs a highly
> consistent set of metadata, and a slightly older version of the file system
> confuses it.
> One defense is to use snapshots. However, this works at the table level, and
> it is hard to coordinate with the HDFS snapshot.
> Another approach is to leave a short history of the files in the !METADATA
> table. The Google paper hints at keeping historical information:
> {quote}
> We also store secondary information in the
> METADATA table, including a log of all events per-
> taining to each tablet (such as when a server begins
> serving it). This information is helpful for debugging
> and performance analysis.
> {quote}
> I think it would also be helpful for disaster recovery. It may require the
> GC to be more sensitive to historical information about compactions.
> Alternatively, we should start looking into high-availability NNs and
> bookkeeper high-performance logging.
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