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Michael Smith commented on HBASE-28595: --------------------------------------- I saw the OutOfOrderScannerException while working on various iterations of reproduction. I think it would cover the case of a successful scan then lost response; the client would retry, get OutOfOrderScannerException, and recognize it needs to reset the scanner. > 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 > Labels: pull-request-available > > 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 at the same time, the client gets an rpc connection > closed error and doesn't process the exception sent by the server. Client > then thinks it got a network error, which leads to retrying the RPC instead > of opening a new scanner. But then when the client retry reaches the server, > the server returns an empty ScanResponse instead of an error, 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. -- This message was sent by Atlassian Jira (v8.20.10#820010)