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https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12845724#action_12845724
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stack commented on HBASE-2248:
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Yeah, I just tried to run test suite and ran into at least the TestHeapSize
failures.
On a test up on cluster, something is up. Its not deadlocked but its only
making slow progress. Regionservers are all waiting for something to do. Will
look in morning.
On the patch:
+ "aka DNC" ... whats DNC? (Democratic National Committee?)
+ In KV, it has "+ * @deprecated" Usually deprecated points helpfully to
what should be used instead. What should folks use instead of createFirstOnRow
override?
+ +1 on this comment of yours "+ // TODO the family and qualifier should
be compared separately"
+ So, on flush of the MemStore, we don't need to clean out items that MemStore
Deletes effect? We now let go of the old axiom that Deletes in storefiles only
apply to storefiles that follow and not to the current storefile?
+ I love all the stuff removed.
More review later.
What do we see as implications of removal of the special Get-code path?
+ Is it true that now, you can do inserts where timestamps are out of order?
(If no deletes?) If so, don't we need unit tests to prove this assertion?
+ What about performance? Though the new Get-Scan does storefile accesses in
parallel, if > N storefiles, if looking for latest version only, we'll be
slower (at least until we add BFs?).
> 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-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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