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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2162) scanners need to obey row locks, a modest propsal
Date Sat, 23 Jan 2010 07:23:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12804030#action_12804030
] 

ryan rawson commented on HBASE-2162:
------------------------------------

If we want to replace get with a 1 row scan, we might have to do this work. with my thoughts,
it might be low cost to do a rippling lock.

Another alternative is to use a data structure that prevents half-rows from being read by
scanners.

This is a dangerous area we can and should do better in imho. The time is nigh!

> scanners need to obey row locks, a modest propsal
> -------------------------------------------------
>
>                 Key: HBASE-2162
>                 URL: https://issues.apache.org/jira/browse/HBASE-2162
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: ryan rawson
>            Assignee: ryan rawson
>             Fix For: 0.21.0
>
>
> 15:54 < dj_ryan> - next:
> 15:54 < dj_ryan> do next on Tree in memstore get rowid
> 15:55 < dj_ryan> acquire read lock on rowid (wait if necessary)
> 15:55 < dj_ryan> snapshot the entire row worth of data from memstore into scanner
> 15:55 < dj_ryan> release read lock on rowid
> 15:56 < dj_ryan> so if we get an insert on a row after the 'do next' which would
call 'next' on the 
>                  previous last value grabbed from the tree
> 15:56 < dj_ryan> we'd skip that one
> 15:56 < dj_ryan> which is fine
> 15:57 < dj_ryan> i guess the issue comes in when you have to next a bunch to get
to the next row
> 15:57 < dj_ryan> but that is doable with a simple little while loop
> 15:57 < dj_ryan> this only applies to memstore
> 15:57 < dj_ryan> snapshot = hfile 
> 15:57 < dj_ryan> since its immutable

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