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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15021607#comment-15021607
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stack commented on HBASE-13082:
-------------------------------
You think we need to do checkFlushed(); on each seek call? Would doing it
on next be enough? Does checkReseek end up calling seek? (Which calls
checkFlushed?) Yeah, how often we calling checkFlushed? The less the better.
I love the removal of all those locks. Looks beautiful.
Is checkFlushed the right name for the method? I see you set flushed to true in
670 flushed = true; in updateReaders ... so should it be
checkReadersChanged or checkResetStoreFiles or something?
Yeah, why call checkFlushed in shipped? Is that a good place to do it? I'm
wondering why we'd call checkFlushed in any place but on the way out of a next
call?
Why is it a CompactedHFilesCleaner cleaner and not a HFileCleaner? Is it a
Cleaner? It closes storefiles. Discharger as in it is discharging the hfile
from duty... not it is eligable for archiving... and later delete? Or Acquiter
I think this patch is almost there and its a very nice one.
> 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.pdf,
> HBASE-13082_12.patch, HBASE-13082_13.patch, HBASE-13082_14.patch,
> HBASE-13082_15.patch, HBASE-13082_1_WIP.patch, HBASE-13082_2.pdf,
> HBASE-13082_2_WIP.patch, HBASE-13082_3.patch, HBASE-13082_4.patch,
> HBASE-13082_9.patch, HBASE-13082_9.patch, HBASE-13082_withoutpatch.jpg,
> HBASE-13082_withpatch.jpg, LockVsSynchronized.java, 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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