Sailesh Mukil has posted comments on this change.

Change subject: IMPALA-5198: Error messages are sometimes dropped before 
reaching client
......................................................................


Patch Set 4:

> > > (1 comment)
 > 
 > > We have an error_log, which is different from error messages,
 > which
 > > is different from error details. There is a lot of overlap
 > between
 > > these which results in quite some confusion.
 > >
 > > The error_log is populated when we call LogError(). The error
 > > message is the error associated with a status error. The error
 > > details are extra error messages that we attach to a status.
 > >
 > 
 > Note that the error_log is really more like a warning log. i.e.
 > these "errors" don't necessarily cause query execution to abort.
 > 
That's not always the case. In some places we add actual errors to the 
error_log like here:
https://github.com/apache/incubator-impala/blob/master/be/src/runtime/plan-fragment-executor.cc#L343

 > > Cumulatively, all tests together end up relying on all 3 of these
 > > being returned. Before this patch, the error_log was never being
 > > printed, but due to the overlap with the error message from the
 > > status, all the tests passed. Now, that we print the error_log
 > with
 > > this patch, a lot of errors get printed twice, which looks ugly.
 > >
 > 
 > Where does this patch cause the error log to be printed? And what
 > do you mean by "printed"?
 > 
Printed meaning, returned to the client, so it prints on the client's end 
(impala-shell)

 > Also, concerning the original issue, in what cases are error
 > message being dropped?

When we unpack messages from the TStatus object into a Status object, we don't 
copy the original ErrorMsg::message_ back to the new message_, instead we put 
everything in details_ causing the message not to be printed (returned to the 
client), because GetErrorLog() only looks at ErrorMsg::message_ and not 
details_.

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Gerrit-MessageType: comment
Gerrit-Change-Id: I5d9d63610eb0d2acae3a9303ce46e1410727ce87
Gerrit-PatchSet: 4
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Sailesh Mukil <[email protected]>
Gerrit-Reviewer: Dan Hecht <[email protected]>
Gerrit-Reviewer: Matthew Jacobs <[email protected]>
Gerrit-Reviewer: Sailesh Mukil <[email protected]>
Gerrit-Reviewer: Tim Armstrong <[email protected]>
Gerrit-HasComments: No

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