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https://issues.apache.org/jira/browse/HBASE-28595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17846649#comment-17846649
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Duo Zhang commented on HBASE-28595:
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By design, if the server side has already closed the scanner, the retry RPC
should receive a UnknownScannerException.
Let me check the code.
Thanks for providing this.
> Losing exception from scan RPC can lead to partial results
> ----------------------------------------------------------
>
> Key: HBASE-28595
> URL: https://issues.apache.org/jira/browse/HBASE-28595
> Project: HBase
> Issue Type: Bug
> Components: Client, regionserver, Scanners
> Reporter: Csaba Ringhofer
> Assignee: Csaba Ringhofer
> Priority: Critical
>
> This was discovered in Apache Impala using HBase 2.2 based branch hbase
> client and server. It is not clear yet whether other branches are also
> affected.
> The issue happens if the server side of the scan throws an exception and
> closes the scanner, but the client doesn't get the exact exception and it
> treats it as network error, which leads to retrying the RPC instead of
> opening a new scanner. In this case the server returns an empty ScanResponse
> instead of an error when the RPC is retried, leading to closing the scanner
> on client side without returning any error.
> A few pointers to critical parts:
> region server:
> 1st call throws exception leading to closing (but not deleting) scanner:
> https://github.com/apache/hbase/blob/0c8607a35008b7dca15e9daaec41ec362d159d67/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java#L3539
> 2nd call (retry of 1st) returns empty results:
> https://github.com/apache/hbase/blob/0c8607a35008b7dca15e9daaec41ec362d159d67/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java#L3403
> client:
> some exceptions are handled as non-retriable at RPC level and are only
> handled through opening a new scanner:
> https://github.com/apache/hbase/blob/0c8607a35008b7dca15e9daaec41ec362d159d67/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ScannerCallable.java#L214
> https://github.com/apache/hbase/blob/0c8607a35008b7dca15e9daaec41ec362d159d67/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClientScanner.java#L367
> This mechanism in the client only works if it gets the exception from the
> server. If there are connection issues during the RPC then the client won't
> really know the state of the server.
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