Christopher Channing has uploaded a new patch set (#2).

Change subject: IMPALA-3964: Remove erroneous DCHECK in Parquet scanner.
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IMPALA-3964: Remove erroneous DCHECK in Parquet scanner.

The Bug: Prior to this patch, a DCHECK was used to verify that the
underlying memory pool for the scratch batch was empty in a count based
scenario. For IMPALA-3964 (where a count(*) is performed over a nested
collection), if a Parquet column chunk is compressed, upon reading each
new data page it would be decompressed and eventually placed in to the
underlying scratch batch memory pool causing the aforementioned DCHECK
to fail. This was not picked up in the test suite as the TPCH nested
Parquet data is not compressed.

The Fix: Removed the erroneous DCHECK. Added logic to determine if any
remaining tuple pointers need to be moved to the destination row batch.
Augmented the load_nested.py script to snappy compress each of the
tables within the 'tpch_nested_parquet' database. Note, no new tests
are needed as there are already a number of existing functional nested
Parquet tests that cover this scenario.

Change-Id: Id0955c85d18dfba4bd29a35ec95d0355da050607
---
M be/src/exec/hdfs-parquet-scanner.cc
M testdata/bin/load_nested.py
2 files changed, 8 insertions(+), 1 deletion(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/40/3940/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Id0955c85d18dfba4bd29a35ec95d0355da050607
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Christopher Channing <[email protected]>
Gerrit-Reviewer: Alex Behm <[email protected]>

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