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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2248) Provide new non-copy mechanism to assure atomic reads in get and scan
Date Mon, 19 Apr 2010 14:48:06 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12858527#action_12858527

Andrew Purtell commented on HBASE-2248:

   [[ Old comment, sent by email on Wed, 14 Apr 2010 04:52:37 +0000 ]]

Thanks Ryan! Testing now.

> Provide new non-copy mechanism to assure atomic reads in get and scan
> ---------------------------------------------------------------------
>                 Key: HBASE-2248
>                 URL: https://issues.apache.org/jira/browse/HBASE-2248
>             Project: Hadoop HBase
>          Issue Type: Bug
>    Affects Versions: 0.20.3
>            Reporter: Dave Latham
>            Assignee: ryan rawson
>            Priority: Blocker
>             Fix For: 0.20.4
>         Attachments: HBASE-2248-demonstrate-previous-impl-bugs.patch, HBASE-2248-GetsAsScans3.patch,
HBASE-2248-no-row-locks.txt, HBASE-2248-rr-final1.txt, HBASE-2248-rr-pre-durability4.txt,
hbase-2248.gc, HBASE-2248.patch, hbase-2248.txt, profile.png, put_call_graph.png, readownwrites-lost.2.patch,
readownwrites-lost.patch, Screen shot 2010-02-23 at 10.33.38 AM.png, threads.txt
> HBASE-2037 introduced a new MemStoreScanner which triggers a ConcurrentSkipListMap.buildFromSorted
clone of the memstore and snapshot when starting a scan.
> After upgrading to 0.20.3, we noticed a big slowdown in our use of short scans.  Some
of our data repesent a time series.   The data is stored in time series order, MR jobs often
insert/update new data at the end of the series, and queries usually have to pick up some
or all of the series.  These are often scans of 0-100 rows at a time.  To load one page, we'll
observe about 20 such scans being triggered concurrently, and they take 2 seconds to complete.
 Doing a thread dump of a region server shows many threads in ConcurrentSkipListMap.biuldFromSorted
which traverses the entire map of key values to copy it.  

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