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https://issues.apache.org/jira/browse/HBASE-19468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16288755#comment-16288755
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Anoop Sam John commented on HBASE-19468:
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I think the assumption here is that eventually next() or so will be called and
at that time scanner to be opened. So this is an eager open. But I do have a
concern whether this is correct. May be it was a get op and no other next()
calls might happen? Even on Scan. Would be best to go by the old way of open
scanner on the new files when really needed. The eager open is to make the ref
count incremented. The patch is simple but not really in line with the way.
That is why I was wondering whether we can have a similar way of update readers
after compaction(like the flush) and clear these new files from list.. Oh ya we
should have ways of notify
> FNFE during scans and flushes
> -----------------------------
>
> Key: HBASE-19468
> URL: https://issues.apache.org/jira/browse/HBASE-19468
> Project: HBase
> Issue Type: Sub-task
> Components: regionserver, Scanners
> Affects Versions: 1.3.1
> Reporter: Thiruvel Thirumoolan
> Priority: Critical
> Fix For: 2.0.0, 1.4.1, 1.5.0, 1.3.3
>
> Attachments: HBASE-19468-poc.patch, HBASE-19468_1.4.patch
>
>
> We see FNFE exceptions on our 1.3 clusters when scans and flushes happen at
> the same time. This causes regionserver to throw a UnknownScannerException
> and client retries.
> This happens during the following sequence:
> 1. Scanner open, client fetched some rows from regionserver and working on it
> 2. Flush happens and storeScanner is updated with flushed files
> (StoreScanner.updateReaders())
> 3. Compaction happens on the region while scanner is still open
> 4. compaction discharger runs and cleans up the newly flushed file as we
> don't have new scanners on it yet.
> 5. Client issues scan.next and during StoreScanner.resetScannerStack(), we
> get a FNFE. RegionServer throws a UnknownScannerThe client retries in 1.3.
> With branch-1.4, the scan fails with a DoNotRetryIOException.
> [~ram_krish], My proposal is to increment the reader count during
> updateReaders() and decrement it during resetScannerStack(), so discharger
> doesn't clean it up. Scan lease expiries also have to be taken care of. Am I
> missing anything? Is there a better approach?
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