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Date: Sun, 29 Dec 2013 03:04:53 +0000 (UTC)
From: "Feng Honghua (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12686132.1387794060587.19315.1388286293809@arcas>
In-Reply-To: <JIRA.12686132.1387794060587@arcas>
References: <JIRA.12686132.1387794060587@arcas>
Subject: [jira] [Commented] (HBASE-10227) When a region is opened, its mvcc
 isn't correctly recovered when there are split hlogs to replay
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    [ https://issues.apache.org/jira/browse/HBASE-10227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13858222#comment-13858222 ] 

Feng Honghua commented on HBASE-10227:
--------------------------------------

[~gustavoanatoly] : sounds good. I will also try to find time to extract the original fix for it from jira-8721 these days to attach here for your reference.

> When a region is opened, its mvcc isn't correctly recovered when there are split hlogs to replay
> ------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-10227
>                 URL: https://issues.apache.org/jira/browse/HBASE-10227
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>            Reporter: Feng Honghua
>            Assignee: Gustavo Anatoly
>
> When opening a region, all stores are examined to get the max MemstoreTS and it's used as the initial mvcc for the region, and then split hlogs are replayed. In fact the edits in split hlogs have kvs with greater mvcc than all MemstoreTS in all store files, but replaying them don't increment the mvcc according at all. From an overall perspective this mvcc recovering is 'logically' incorrect/incomplete.
> Why currently it doesn't incur problem is because no active scanners exists and no new scanners can be created before the region opening completes, so the mvcc of all kvs in the resulted hfiles from hlog replaying can be safely set to zero. They are just treated as kvs put 'earlier' than the ones in HFiles with mvcc greater than zero(say 'earlier' since they have mvcc less than the ones with non-zero mvcc, but in fact they are put 'later'), and without any incorrect impact just because during region opening there are no active scanners existing / created.
> This bug is just in 'logic' sense for the time being, but if later on we need to survive mvcc in the region's whole logic lifecycle(across regionservers) and never set them to zero, this bug needs to be fixed first.


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