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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HBASE-2248) Provide new non-copy mechanism to assure atomic reads in get and scan
Date Fri, 05 Mar 2010 03:27:27 GMT

     [ https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HBASE-2248:
-------------------------------

    Attachment: readownwrites-lost.2.patch

Here's a slightly better test patch, much more sure to fail.

(this test could easily be written without multiple threads, but as an illustration of the
client's view of the consistency, the threads are useful)

> 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-ryan.patch,
hbase-2248.gc, HBASE-2248.patch, 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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