Philip Zeyliger c9740b43d1 IMPALA-5908: Allow SET to unset modified query options. ...

The query 'SET <option>=""' will now unset an option within the session,
reverting it to its default state.

This change became necessary when "SET" started returning an empty
string for unset options which don't have a default. The test
infrastructure (impala_test_suite.py) resets options to what it thinks
is its defaults, and, when this broke, some ASAN builds started to fail,
presumably due to a timing issue with how we re-use connections between
tests.

Previously, SessionState copied over the default options from the server
when the session was created and then mutated that. To support unsetting
options at the session layer, this change keeps a pointer to the default
server settings, keeps separately the mutations, and overlays the
options each time they're requested. Similarly, for configuration
overlays that happen per-query, the overlay is now done explicitly,
because empty per-query overlay values (key=..., value="") now have no effect.

Because "set key=''" is ambiguous between "set to the empty string" and
"unset", it's now impossible to set to the empty string, at the session
layer, an option that is configured at a previous layer. In practice,
this is just debug_action and request_pool. debug_action is essentially
an internal tool. For request_pool, this means that setting the default
request_pool via impalad command line is now a bad idea, as it can't
be cleared at a per-session level. For request_pool, the correct
course of action for users is to use placement rules, and to have a
default placement rule.

Testing:
* Added a simple test that triggered this side-effect without this code.
  Specifically, "impala-python infra/python/env/bin/py.test tests/metadata/test_set.py -s"
  with the modified set.test triggers.
* Amended tests/custom_cluster/test_admission_controller.py; it was
  useful for testing these code paths.
* Added cases to query-options-test to check behavior for both
  defaulted and non-defaulted values.
* Added a custom cluster test that checks that overlays are
  working against
* Ran an ASAN build where this was triggering previously.

Change-Id: Ia8c383e68064f839cb5000118901dff77b4e5cb9
Reviewed-on: http://gerrit.cloudera.org:8080/8070
Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com>
Tested-by: Impala Public Jenkins

2017-10-05 03:04:38 +00:00

6.8 KiB

Raw Blame History

View Raw