[Impala-ASF-CR] IMPALA-5589: change "set" in impala-shell to show empty string for unset query options

["Philip Zeyliger (Code Review)" <ge...@cloudera.org>]

Philip Zeyliger has uploaded a new patch set (#2).

Change subject: IMPALA-5589: change "set" in impala-shell to show empty string for unset query options
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IMPALA-5589: change "set" in impala-shell to show empty string for unset query options

When converting TQueryOptions to a map<string,string>, we now convert
unset options to the empty string. Within TQueryOptions we have optional
options (like mt_dop or compression_codec) with no default specified. In
this case, the user was seeing 0 for numeric types and the first enum
option for enumeration types (e.g., "NONE" in the compression case).
This was confusing as the implementation handles this "null" case
differently (e.g., using SNAPPY as the default codec in the case
reported in the JIRA).

When running "set" in impala-shell, the difference is as
follows:

    -        BUFFER_POOL_LIMIT: [0]
    +        BUFFER_POOL_LIMIT: []
    -        COMPRESSION_CODEC: [NONE]
    +        COMPRESSION_CODEC: []
    -        MT_DOP: [0]
    +        MT_DOP: []
    -        RESERVATION_REQUEST_TIMEOUT: [0]
    +        RESERVATION_REQUEST_TIMEOUT: []
    -        SEQ_COMPRESSION_MODE: [0]
    +        SEQ_COMPRESSION_MODE: []
    -        V_CPU_CORES: [0]
    +        V_CPU_CORES: []

Obviously, the empty string is a valid value for a string-typed option, where
it will be impossible to tell the difference between "unset" and "set to empty
string." Today, there are two string-typed options: debug_string defaults to ""
and request_pool has no default. An alternative would have been to use
a special token like "_unset" or to introduce a new field in the beeswax
Thrift ConfigVariable struct. I think the simply empty string approach
is clearest.

The other users of this state, which I believe are HiveServer2's OpenSession()
call and HiveServer2's response to a "SET" query are affected. They
beneift from the same fix, and a new test has been added to test_hs2.py.

I did a mild refactoring in the HS2 tests to write a helper method
for the very common pattern of excecuting a query.

Testing:
* Manual testing with impala-shell
* Modified impala-shell tests to check this explicitly for one case.
* Modified HS2 test to check this as well as the SET k=v statement,
  which looked otherwise untested.

Change-Id: I86bc06a58d67b099da911293202dae9e844c439b
---
M be/src/service/query-options-test.cc
M be/src/service/query-options.cc
M be/src/service/query-options.h
M tests/hs2/hs2_test_suite.py
M tests/hs2/test_hs2.py
M tests/shell/test_shell_commandline.py
6 files changed, 94 insertions(+), 48 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/86/7886/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I86bc06a58d67b099da911293202dae9e844c439b
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Philip Zeyliger <ph...@cloudera.com>
Gerrit-Reviewer: Matthew Jacobs <mj...@cloudera.com>
Gerrit-Reviewer: Philip Zeyliger <ph...@cloudera.com>