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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2248) Provide new non-copy mechanism to assure atomic reads in get and scan
Date Wed, 14 Apr 2010 05:32:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12856759#action_12856759
] 

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

This last patch is looking good.  The spin lock slowing writes is gone it looks like and most
of the tests are passing.  Will report more in morning.  Will let tests run overnight.

> 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-rr-alpha3.txt, HBASE-2248-rr-pre-durability2.txt, HBASE-2248-rr-pre-durability3.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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