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From "Feng Honghua (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10227) When a region is opened, its mvcc isn't correctly recovered when there are split hlogs to replay
Date Sun, 29 Dec 2013 03:10:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13858224#comment-13858224
] 

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

thanks [~yuzhihong@gmail.com] for directing. I just took a look at 10241, seems it together
with 8763 is a bit general, while this one is pretty specific , its fix can be a part of those
general jiras, so I think it's ok to fix this one separately, opinion? :-)

> 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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