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https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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stack resolved HBASE-2248.
--------------------------
Hadoop Flags: [Incompatible change, Reviewed]
Release Note: This patch changes the Get code path to instead be a Scan of
one row. This means than inserting cells out of timestamp order should work
now (tests to verify to follow part of hbase-2294) but also that a delete at an
explicit timestamp now overshadows EVEN if the effected cell is put after the
delete (The old Get code path did early-out so a subsequent puts would not see
the delete).
Resolution: Fixed
Thanks all who contributed to this issue: Todd, Dan, Yoram and in particular
Ryan.
> 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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