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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14963400#comment-14963400
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Anoop Sam John commented on HBASE-13082:
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Good doc explaining the change.
bq. Along with the ref count, we also have CompactionStatus (COMPACTED and
NON_COMPACTED) added to these store file readers
This status is in reader? It suits better in StoreFile no? Even the ref count
is in reader? I would say it is better suited in StoreFile. That call the
state as Compacted we better call it as a file to be discarded? When we mark a
file as compacted the confusion can be like whether this file is a file created
out of compaction. (?)
bq. Ensure that a background thread runs periodically runs that scans the list
of store files and checks for the state as COMPACTED...
This is a new Chore thread adding to the system.. Mention about it clearly. It
will be one thread per RS. Also what is its interval? Is it configurable? How?
bq.Hence it requires us to add new APIs which ensures that a split can go ahead
even if reference files are present but they are in the COMPACTED state
hmm.. making this more complex :-)
> Coarsen StoreScanner locks to RegionScanner
> -------------------------------------------
>
> Key: HBASE-13082
> URL: https://issues.apache.org/jira/browse/HBASE-13082
> Project: HBase
> Issue Type: Bug
> Reporter: Lars Hofhansl
> Assignee: ramkrishna.s.vasudevan
> Attachments: 13082-test.txt, 13082-v2.txt, 13082-v3.txt,
> 13082-v4.txt, 13082.txt, 13082.txt, HBASE-13082.pdf, HBASE-13082_1_WIP.patch,
> HBASE-13082_2_WIP.patch, HBASE-13082_3.patch, HBASE-13082_4.patch, gc.png,
> gc.png, gc.png, hits.png, next.png, next.png
>
>
> Continuing where HBASE-10015 left of.
> We can avoid locking (and memory fencing) inside StoreScanner by deferring to
> the lock already held by the RegionScanner.
> In tests this shows quite a scan improvement and reduced CPU (the fences make
> the cores wait for memory fetches).
> There are some drawbacks too:
> * All calls to RegionScanner need to be remain synchronized
> * Implementors of coprocessors need to be diligent in following the locking
> contract. For example Phoenix does not lock RegionScanner.nextRaw() and
> required in the documentation (not picking on Phoenix, this one is my fault
> as I told them it's OK)
> * possible starving of flushes and compaction with heavy read load.
> RegionScanner operations would keep getting the locks and the
> flushes/compactions would not be able finalize the set of files.
> I'll have a patch soon.
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