[Impala-ASF-CR] IMPALA-4285/IMPALA-4286: Fixes for Parquet scanner with MT DOP > 0.

["Alex Behm (Code Review)" <ge...@cloudera.org>]

Hello Dan Hecht,

I'd like you to reexamine a change.  Please visit

    http://gerrit.cloudera.org:8080/4767

to look at the new patch set (#4).

Change subject: IMPALA-4285/IMPALA-4286: Fixes for Parquet scanner with MT_DOP > 0.
......................................................................

IMPALA-4285/IMPALA-4286: Fixes for Parquet scanner with MT_DOP > 0.

IMPALA-4258: The problem was that there was a reference to
HdfsScanner::batch_ hidden inside WriteEmptyTuples(). The batch_
reference is NULL when the scanner is run with MT_DOP > 1.

IMPALA-4286: When there are no scan ranges HdfsScanNodeBase::Open()
exits early without initializing the reader context. This lead to
a DCHECK in IoMgr::GetNextRange() called from HdfsScanNodeMt.
The fix is to short-circuit the empty scan range case in
HdfsScanNodeMt::GetNext().

I combined these two bugfixes because the new basic test covers
both cases.

Testing: Added a new test_mt_dop.py test.

Change-Id: I79c0f6fd2aeb4bc6fa5f87219a485194fef2db1b
---
M be/src/exec/hdfs-avro-scanner.cc
M be/src/exec/hdfs-parquet-scanner.cc
M be/src/exec/hdfs-rcfile-scanner.cc
M be/src/exec/hdfs-scan-node-mt.cc
M be/src/exec/hdfs-scanner.cc
M be/src/exec/hdfs-scanner.h
M be/src/exec/hdfs-sequence-scanner.cc
M be/src/exec/hdfs-text-scanner.cc
A testdata/workloads/functional-query/queries/QueryTest/mt-dop.test
A tests/query_test/test_mt_dop.py
10 files changed, 88 insertions(+), 62 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/67/4767/4
-- 
To view, visit http://gerrit.cloudera.org:8080/4767
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I79c0f6fd2aeb4bc6fa5f87219a485194fef2db1b
Gerrit-PatchSet: 4
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Alex Behm <al...@cloudera.com>
Gerrit-Reviewer: Alex Behm <al...@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dh...@cloudera.com>