[SPARK-11787][SQL] Improve Parquet scan performance when using flat schemas.

This patch adds an alternate to the Parquet RecordReader from the parquet-mr project
that is much faster for flat schemas. Instead of using the general converter mechanism
from parquet-mr, this directly uses the lower level APIs from parquet-columnar and a
customer RecordReader that directly assembles into UnsafeRows.

This is optionally disabled and only used for supported schemas.

Using the tpcds store sales table and doing a sum of increasingly more columns, the results
are:

For 1 Column:
  Before: 11.3M rows/second
  After: 18.2M rows/second

For 2 Columns:
  Before: 7.2M rows/second
  After: 11.2M rows/second

For 5 Columns:
  Before: 2.9M rows/second
  After: 4.5M rows/second

Author: Nong Li <nong@databricks.com>

Closes #9774 from nongli/parquet.

0 files changed, 0 insertions, 0 deletions