[jira] Commented: (HBASE-2248) Provide new non-copy mechanism to assure atomic reads in get and scan

["stack (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854828#action_12854828 ] 

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

Can we have a version for 0.20_pre_durability branch Ryan?  There are a bunch of failures all in HRegion.  Some I can sort of make sense of but others would take me a while to figure.  You know the code so would probably take you short amount of time?

> 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
>            Priority: Blocker
>             Fix For: 0.20.4
>
>         Attachments: HBASE-2248-demonstrate-previous-impl-bugs.patch, HBASE-2248-GetsAsScans3.patch, HBASE-2248-rr-alpha1.txt, HBASE-2248-rr-alpha2.txt, HBASE-2248-rr-alpha3.txt, 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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