[jira] [Work started] (IMPALA-12014) Output a warning message on failed KeepAlive RPC for a Kudu scanner

["Alexey Serbin (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-12014?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on IMPALA-12014 started by Alexey Serbin.
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> Output a warning message on failed KeepAlive RPC for a Kudu scanner
> -------------------------------------------------------------------
>
>                 Key: IMPALA-12014
>                 URL: https://issues.apache.org/jira/browse/IMPALA-12014
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Backend, be
>    Affects Versions: Impala 2.7.0, Impala 2.8.0, Impala 2.7.1, Impala 2.9.0, Impala 2.10.0, Impala 2.11.0, Impala 3.0, Impala 2.12.0, Impala 3.1.0, Impala 3.2.0, Impala 4.0.0, Impala 3.3.0, Impala 3.4.0, Impala 3.4.1, Impala 4.1.0, Impala 4.0.1, Impala 4.2.0, Impala 4.1.1
>            Reporter: Alexey Serbin
>            Assignee: Alexey Serbin
>            Priority: Minor
>              Labels: supportability, troubleshooting
>
> With [IMPALA-3292|https://issues.apache.org/jira/browse/IMPALA-3292], the code has been modified to ignore failed KeepAlive RPCs for Kudu scanners because one of the follow-up KeepAlive RPCs usually succeeds within TTL for an idle Kudu scanner.
> However, if a Kudu tablet server had been busy for a long time, it might happen that all the consecutive KeepAlive requests failed as well (e.g., if the RPC queue stayed full for the whole interval of the scanner TTL).  If so happened, the corresponding Impala query would fail with an error message in the Impala's query profile like below:
> {noformat}
> ...
>     Query Type: QUERY
>     Query State: EXCEPTION
>     Impala Query State: ERROR
>     Query Status: Unable to advance iterator for node with id '1' for Kudu table 'mega_table': Not found: Scanner 4235dd17eb444a36a945f003c23dcf81 not found (it may have expired)
> ...
> {noformat}
> Without a warning message logged by impalad or other clues it's hard to infer the root cause of such a situation for people who have not much knowledge of the Kudu specifics.
> It would be great to at least log a warning message about failed attempts to send KeepAlive RPC for Kudu scanners.  As of now, the message is logged with {{VLOG(1)}} facility, but verbose logging isn't usually enabled by default for impalad.



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