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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 16:16:32 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749962#action_12749962
] 

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

These kinds of race conditions are another reason why moving stuff into ZK will make life
easier.  Do you think we need to do something major for 0.20 or can we wait for 0.21?

> 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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