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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-10958) [dataloss] Bulk loading with seqids can prevent some log entries from being replayed
Date Fri, 18 Apr 2014 00:42:18 GMT

     [ https://issues.apache.org/jira/browse/HBASE-10958?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jean-Daniel Cryans updated HBASE-10958:
---------------------------------------

    Attachment: HBASE-10958-0.94.patch
                HBASE-10958-v3.patch

Attaching 2 patches.

One is a backport for 0.94. While doing the backport I saw that a TestSnapshotFromMaster was
failing and Matteo was able to see that it was an error in my patch, flushing always returned
that it needed compaction. I need to rerun all the tests now but it was the only one that
failed (haven't tried with security either). I also added a test in TestHRegion for that.

The second patch is for trunk, in which I ported the same test to TestHRegion. Interestingly,
it didn't work. I found that in 0.94 we compact if num_files > compactionThreshold, but
in trunk it's >=, so it seems that we compact more often now. This patch also has the fixes
from [~stack]'s comments.

> [dataloss] Bulk loading with seqids can prevent some log entries from being replayed
> ------------------------------------------------------------------------------------
>
>                 Key: HBASE-10958
>                 URL: https://issues.apache.org/jira/browse/HBASE-10958
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.96.2, 0.98.1, 0.94.18
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jean-Daniel Cryans
>            Priority: Blocker
>             Fix For: 0.99.0, 0.94.19, 0.98.2, 0.96.3
>
>         Attachments: HBASE-10958-0.94.patch, HBASE-10958-less-intrusive-hack-0.96.patch,
HBASE-10958-quick-hack-0.96.patch, HBASE-10958-v2.patch, HBASE-10958-v3.patch, HBASE-10958.patch
>
>
> We found an issue with bulk loads causing data loss when assigning sequence ids (HBASE-6630)
that is triggered when replaying recovered edits. We're nicknaming this issue *Blindspot*.
> The problem is that the sequence id given to a bulk loaded file is higher than those
of the edits in the region's memstore. When replaying recovered edits, the rule to skip some
of them is that they have to be _lower than the highest sequence id_. In other words, the
edits that have a sequence id lower than the highest one in the store files *should* have
also been flushed. This is not the case with bulk loaded files since we now have an HFile
with a sequence id higher than unflushed edits.
> The log recovery code takes this into account by simply skipping the bulk loaded files,
but this "bulk loaded status" is *lost* on compaction. The edits in the logs that have a sequence
id lower than the bulk loaded file that got compacted are put in a blind spot and are skipped
during replay.
> Here's the easiest way to recreate this issue:
>  - Create an empty table
>  - Put one row in it (let's say it gets seqid 1)
>  - Bulk load one file (it gets seqid 2). I used ImporTsv and set hbase.mapreduce.bulkload.assign.sequenceNumbers.
>  - Bulk load a second file the same way (it gets seqid 3).
>  - Major compact the table (the new file has seqid 3 and isn't considered bulk loaded).
>  - Kill the region server that holds the table's region.
>  - Scan the table once the region is made available again. The first row, at seqid 1,
will be missing since the HFile with seqid 3 makes us believe that everything that came before
it was flushed.



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