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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2248) Provide new non-copy mechanism to assure atomic reads in get and scan
Date Fri, 12 Mar 2010 05:47:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844378#action_12844378
] 

ryan rawson commented on HBASE-2248:
------------------------------------

Yes I have asked Todd and rolled up his patch. I have identified a small
race condition in scanning today and ill fix it soon and likely post on
Monday.

On Mar 12, 2010 12:25 AM, "stack (JIRA)" <jira@apache.org> wrote:


   [
https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844367#action_12844367]

stack commented on HBASE-2248:
------------------------------

@Ryan, your next patch picks up Todds spin-wait I believe?

HBASE-2248-ryan.patch, hbase-2248.gc, HBASE-2248.patch, hbase-2248.txt,
readownwrites-lost.2.patch, readownwrites-lost.patch, Screen shot 2010-02-23
at 10.33.38 AM.png, threads.txt
ConcurrentSkipListMap.buildFromSorted clone of the memstore and snapshot
when starting a scan.
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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> 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
>             Fix For: 0.20.4
>
>         Attachments: HBASE-2248-demonstrate-previous-impl-bugs.patch, HBASE-2248-GetsAsScans3.patch,
HBASE-2248-ryan.patch, hbase-2248.gc, HBASE-2248.patch, hbase-2248.txt, 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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