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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18042) Client Compatibility breaks between versions 1.2 and 1.3
Date Mon, 22 May 2017 13:58:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16019602#comment-16019602

Duo Zhang commented on HBASE-18042:

After digging I think HBASE-17489 did break the compatibility between 1.2 and 1.3. Before
branch-1.2, we only set moreResultsInRegion to false when we return empty result to client,
even if moreRows returned by the RegionScanner is false. That's why we will issue one more
request to a region which has already been exhausted.

And in 1.3, if we set moreResultsInRegion to false when we have also reached the scan caching,
the {{doneWithRegion}} will return false because the countdown is 0 thus a new request to
the same region will be issued.

It is easy to fix at client side. The problem of the old doneWithRegion method is that, we
set serverHasMoreResults to false even if we do not have moreResultsInRegion flag in proto.
 Will prepare a patch soon.

But I'm not sure if we also need to add some dirty code at server side to keep compatible
with the old client without the new patch. I want to define this problem as a bug, but it
is also a pain for users that they must upgrade to the newest version of 1.2 or 1.1 before
upgrading to 1.3 only because of a 'bug' that does not break anything on 1.2 or 1.1...


> Client Compatibility breaks between versions 1.2 and 1.3
> --------------------------------------------------------
>                 Key: HBASE-18042
>                 URL: https://issues.apache.org/jira/browse/HBASE-18042
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.3.1
>            Reporter: Karan Mehta
>            Assignee: Karan Mehta
> OpenTSDB uses AsyncHBase as its client, rather than using the traditional HBase Client.
From version 1.2 to 1.3, the {{ClientProtos}} have been changed. Newer fields are added to
{{ScanResponse}} proto.
> For a typical Scan request in 1.2, would require caller to make an OpenScanner Request,
GetNextRows Request and a CloseScanner Request, based on {{more_rows}} boolean field in the
{{ScanResponse}} proto.
> However, from 1.3, new parameter {{more_results_in_region}} was added, which limits the
results per region. Therefore the client has to now manage sending all the requests for each
region. Further more, if the results are exhausted from a particular region, the {{ScanResponse}}
will set {{more_results_in_region}} to false, but {{more_results}} can still be true. Whenever
the former is set to false, the {{RegionScanner}} will also be closed. 
> OpenTSDB makes an OpenScanner Request and receives all its results in the first {{ScanResponse}}
itself, thus creating a condition as described in above paragraph. Since {{more_rows}} is
true, it will proceed to send next request at which point the {{RSRpcServices}} will throw
{{UnknownScannerException}}. The protobuf client compatibility is maintained but expected
behavior is modified.

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