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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1806) Scanners do not respect row locks; scanner view could return a skewed view on row if ongoing update
Date Tue, 01 Sep 2009 17:04:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749990#action_12749990
] 

Jonathan Gray commented on HBASE-1806:
--------------------------------------

Agree with apurtell.  It's an accepted fact about scanners, from user POV.  But must be addressed
for master/meta, and I think ZK is the right direction.  For now, ugly stuff in HBASE-1784
is fine with me... this is another one of the issues that only rears it's head during high-load,
sustained imports.  But dealing with it in the case it does happen with a Get sounds fine
for now.

> Scanners do not respect row locks; scanner view could return a skewed view on row if
ongoing update
> ---------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-1806
>                 URL: https://issues.apache.org/jira/browse/HBASE-1806
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: stack
>
> What I'm seeing is that BaseScanner misses updates made by an update milliseconds before
-- even hundreds of milliseconds before.  See hbase-1784 where I'm seeing double-assignment
of regions.
> Scanners do not respect row locks.  They should else could return a row with partial
updates committed.  What if a .META. region has tens of storefiles and a scan does a get full
row which takes a long time.  Say an update comes in during this read.  First it will go in
because no row lock is outstanding.  Second, we'll miss the edit given we look at things in
order -- memstore, then each storefile down to the oldest.  What if the update is followed
by an update of server state; e.g. region is moved out of intransition state?  And inside
in same server, say the master, it makes decisions dependent on what it sees when it does
a scanner#next; e.g. BaseScanner checking for assignment?

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