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https://issues.apache.org/jira/browse/HBASE-10060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13835930#comment-13835930
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Lars Hofhansl commented on HBASE-10060:
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The the other way round, no forward progress on replacing the readers until all
compaction/scanning over any involved readers is done. Need to think about
deadlocks.
> Unsynchronized scanning
> -----------------------
>
> Key: HBASE-10060
> URL: https://issues.apache.org/jira/browse/HBASE-10060
> Project: HBase
> Issue Type: Bug
> Reporter: Lars Hofhansl
>
> HBASE-10015 has some lengthy discussion. The solution there ended up
> replacing synchronized with ReentrantLock, which - somewhat surprisingly -
> yielded a non-trivial improvement for tall tables.
> The goal should be to avoid locking in StoreScanner at all. StoreScanner is
> only accessed by a single thread *except* when we have a concurrent flush or
> a compaction, which is rare (we'd acquire and release the lock millions of
> times per second, and compact/flush a few time an hour at the most).
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