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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lars Hofhansl updated HBASE-13082:
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Attachment: 13082.txt
Simple patch. (much like the patch on HBASE-10015).
A bit ugly, because I did not want to change the coprocessor APIs.
Also thought of another drawback:
* Nobody (coprocessor) can use StoreScanner alone anymore (there'd be nothing
to lock), i.e. all access *must* be via Rigi.onScannerImpl or flushes or
compactions). I think that's OK.
Maybe we can make the lock the compactions/flushes and StoreScanner have to
agree upon explicit.
> 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
> Attachments: 13082.txt
>
>
> 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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