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From "Alex Behm (Code Review)" <>
Subject [Impala-CR](cdh5-trunk) PREVIEW: Basic column-wise slot materialization in Parquet scanner.
Date Wed, 13 Apr 2016 15:42:10 GMT
Alex Behm has uploaded a new change for review.

Change subject: PREVIEW: Basic column-wise slot materialization in Parquet scanner.

PREVIEW: Basic column-wise slot materialization in Parquet scanner.

This change is a first step towards a more efficient Parquet scanner.
The focus is on presenting the new code flow that materializes
the table-level slots in a column-wise fashion, without going deep
into actually improving scan efficieny.

After these changes there are several obvious places that should
be optimized to realize efficiency gains.

Summary of changes
- the table-level tuples are materialized in a column-wise fashion
  with new ColumnReader::ReadValueBatch() functions
- this is done by materializing a 'scratch' batch, and transferring
  scratch tuples that survive filters/conjuncts to the output batch
- the tuples of nested collections are still materialized in
  a row-wise fashion using the ColumnReader::ReadValue() function,
  just as before

Mini benchmark
I ran the following queries on a single impalad before and after my
change using a synthetic 'huge_lineitem' table.
I modified to set the number of rows of any row
batch to 0 to focus the measurement on the scan time.

Query options:
set num_scanner_threads=1;
set disable_codegen=true;
set num_nodes=1;

select * from huge_lineitem;
Before: 22.39s
Afer:   18.50s

select * from huge_lineitem where l_linenumber < 0;
Before: 25.11s
After:  20.56s

select * from huge_lineitem where l_linenumber % 2 = 0;
Before: 26.32s
After:  21.82s

Change-Id: I72a613fa805c542e39df20588fb25c57b5f139aa
M be/src/exec/
M be/src/exec/hdfs-parquet-scanner.h
2 files changed, 373 insertions(+), 144 deletions(-)

  git pull ssh:// refs/changes/79/2779/1
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I72a613fa805c542e39df20588fb25c57b5f139aa
Gerrit-PatchSet: 1
Gerrit-Project: Impala
Gerrit-Branch: cdh5-trunk
Gerrit-Owner: Alex Behm <>

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