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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16624) MVCC DeSerialization bug in the HFileScannerImpl
Date Tue, 13 Sep 2016 16:04:21 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15487602#comment-15487602
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stack commented on HBASE-16624:
-------------------------------

+1 on the fix. Good find. Agree a test would be good but rather, we should have a bigger project
that looks for all places where we do this sort of dodgy convertion ...I'd think this sort
of practice, from int to long, would flag in findbugs or other static analysis tools.

> MVCC DeSerialization bug in the HFileScannerImpl
> ------------------------------------------------
>
>                 Key: HBASE-16624
>                 URL: https://issues.apache.org/jira/browse/HBASE-16624
>             Project: HBase
>          Issue Type: Bug
>          Components: HFile
>    Affects Versions: 2.0.0
>            Reporter: deepankar
>            Assignee: deepankar
>            Priority: Blocker
>         Attachments: HBASE-16624.patch
>
>
> My colleague [~naggarwal] found a bug in the deserialization of mvcc from HFile, As a
part of the optimization of deserialization of VLong, we read a int at once but we forgot
to convert it to unsigned one. 
> This would cause issues because once we cross the integer threshold in sequenceId and
a compaction happens we would write MAX_MEMSTORE_TS in the trailer as 0 (because we will be
reading negative values from the file that got flushed with sequenceId > Integer.MAX_VALUE).
And once we have MAX_MEMSTORE_TS as 0, and there are sequenceId values present alongside with
KeyValues the regionserver will now start failing to read the compacted file and thus corruption.

> Interestingly this would happen only on the tables that don't have  DataBlockEncoding
enabled and unfortunately in our case that turned out to be META and a another small table.
> Fix is small (~20 chars) and attached



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