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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13082) Coarsen StoreScanner locks to RegionScanner
Date Tue, 20 Oct 2015 07:24:27 GMT

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ramkrishna.s.vasudevan commented on HBASE-13082:
------------------------------------------------

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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