Alexey Serbin has submitted this change and it was merged. ( 
http://gerrit.cloudera.org:8080/18846 )

Change subject: [Client] Add query id to trace the whole query process
......................................................................

[Client] Add query id to trace the whole query process

In Impala, an SQL is translated into a query plan. The
query plan contains multiple execution units and is
executed at different hosts of a cluster in a distributed
manner. There exists an unique query id to trace the
execution process of every execution unit. It is useful
in analysis of stuck, failed, and otherwise non-performant
queries. Query id can associate all log records in different
hosts, which belongs to one query.

Scanning a Kudu table is split into multiple scan operations
on appropriate tablets, one scanner per tablet. When scanning
a Kudu table using Impala, corresponding scan nodes appear
for every scanner in the Impala's query plan.  Scanner id is
used to trace the scan operation on a tablet.

But there is a gap between Impala and Kudu. We can't trace the
whole scanning process in Kudu of a query originated from Impala.
There is not unique id to associate the execution of all scanners
in Kudu.

Therefore, with this patch it is now possible to post Impala's
query identifier to Kudu, so it can be associated with Kudu's
scanner id. Then we can trace a query from Impala to Kudu for
troubleshooting and debugging.

Change-Id: I9dbae801596726fec1c85ee547128da3179345d9
Reviewed-on: http://gerrit.cloudera.org:8080/18846
Tested-by: Alexey Serbin <[email protected]>
Reviewed-by: Alexey Serbin <[email protected]>
---
M src/kudu/client/client-test.cc
M src/kudu/client/client.cc
M src/kudu/client/client.h
M src/kudu/client/client.proto
M src/kudu/client/scan_token-internal.cc
M src/kudu/client/scan_token-internal.h
M src/kudu/client/scan_token-test.cc
M src/kudu/client/scanner-internal.cc
M src/kudu/tserver/tablet_server-test.cc
M src/kudu/tserver/tablet_service.cc
M src/kudu/tserver/tserver.proto
11 files changed, 197 insertions(+), 13 deletions(-)

Approvals:
  Alexey Serbin: Looks good to me, approved; Verified

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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: merged
Gerrit-Change-Id: I9dbae801596726fec1c85ee547128da3179345d9
Gerrit-Change-Number: 18846
Gerrit-PatchSet: 32
Gerrit-Owner: Wang Xixu <[email protected]>
Gerrit-Reviewer: Abhishek Chennaka <[email protected]>
Gerrit-Reviewer: Alexey Serbin <[email protected]>
Gerrit-Reviewer: Jian Zhang <[email protected]>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Mahesh Reddy <[email protected]>
Gerrit-Reviewer: Tidy Bot (241)
Gerrit-Reviewer: Wang Xixu <[email protected]>
Gerrit-Reviewer: Yifan Zhang <[email protected]>
Gerrit-Reviewer: Yingchun Lai <[email protected]>
Gerrit-Reviewer: Yuqi Du <[email protected]>

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