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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14964695#comment-14964695
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ramkrishna.s.vasudevan commented on HBASE-13082:
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bq.This status is in reader? It suits better in StoreFile no?
The reason for doing this (I just now checked the code once again) is because
when we create a scanner on the Storefile we do it on the reader associated
with the Storefile and not on the store file. So hence do determine whether
this store file can be used in the scanner or not the state and ref count if it
is in the reader it will be easy to use that info. Already info like isBulkLoad
and setSeqId everything is happening on the reader now and not on the
StoreFile. So may be if we can introduce a getStoreFileScanner at the Storefile
level rather than the Reader as how it is currently is, then we can make this
change of adding the ref count and the state to the StoreFile.
> 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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