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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940078#comment-14940078
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ramkrishna.s.vasudevan commented on HBASE-13082:
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bq.I'm a little late to the party but this versioned data structure sounds
neat. If I'm understanding correctly, it sounds like this versioned data
structure would also allow us to remove the lingering lock in updateReaders
(and potentially remove updateReaders completely?).
I totally agree and can see this is going to happen after this change is done.
Just wanted to confirm one thing ,
In case of compaction it is old data but in new file. So there is no problem.
But in case of bulk loaded files, currently in between a scan if a new file is
bulk loaded it gets included, so after this it will not be. is that behavioral
change fine?
> 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, 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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