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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-19468) FNFE during scans and flushes
Date Tue, 12 Dec 2017 18:17:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-19468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16288004#comment-16288004
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Ted Yu commented on HBASE-19468:
--------------------------------

One upside for modifying reference count directly is that we don't incur additional resource
associated with Scanner(s).
In a loaded server, this aspect should be considered.

> 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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