Github user seancxmao commented on a diff in the pull request:
https://github.com/apache/spark/pull/22184#discussion_r213020789
--- Diff: docs/sql-programming-guide.md ---
@@ -1895,6 +1895,10 @@ working with timestamps in `pandas_udf`s to get the
best performance, see
- Since Spark 2.4, File listing for compute statistics is done in
parallel by default. This can be disabled by setting
`spark.sql.parallelFileListingInStatsComputation.enabled` to `False`.
- Since Spark 2.4, Metadata files (e.g. Parquet summary files) and
temporary files are not counted as data files when calculating table size
during Statistics computation.
+## Upgrading From Spark SQL 2.3.1 to 2.3.2 and above
+
+ - In version 2.3.1 and earlier, when reading from a Parquet table, Spark
always returns null for any column whose column names in Hive metastore schema
and Parquet schema are in different letter cases, no matter whether
`spark.sql.caseSensitive` is set to true or false. Since 2.3.2, when
`spark.sql.caseSensitive` is set to false, Spark does case insensitive column
name resolution between Hive metastore schema and Parquet schema, so even
column names are in different letter cases, Spark returns corresponding column
values. An exception is thrown if there is ambiguity, i.e. more than one
Parquet column is matched.
--- End diff --
As a followup to cloud-fan's point, I did a deep dive into read path of
parquet hive serde table. Following is a rough invocation chain:
```
org.apache.spark.sql.hive.execution.HiveTableScanExec
org.apache.spark.sql.hive.HadoopTableReader (extendes
org.apache.spark.sql.hive.TableReader)
org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat (extends
org.apache.hadoop.mapred.FileInputFormat)
org.apache.hadoop.hive.ql.io.parquet.read.ParquetRecordReaderWrapper
(extends org.apache.hadoop.mapred.RecordReader)
parquet.hadoop.ParquetRecordReader
parquet.hadoop.InternalParquetRecordReader
org.apache.hadoop.hive.ql.io.parquet.read.DataWritableReadSupport (extends
parquet.hadoop.api.ReadSupport)
```
Finally, `DataWritableReadSupport#getFieldTypeIgnoreCase` is invoked.
https://github.com/JoshRosen/hive/blob/release-1.2.1-spark2/ql/src/java/org/apache/hadoop/hive/ql/io/parquet/read/DataWritableReadSupport.java#L79-L95
This is why parquet hive serde table always do case-insensitive field
resolution. However, this is a class inside
`org.spark-project.hive:hive-exec:1.2.1.spark2`.
I also found the related Hive JIRA ticket:
[HIVE-7554: Parquet Hive should resolve column names in case insensitive
manner](https://issues.apache.org/jira/browse/HIVE-7554)
BTW:
* org.apache.hadoop.hive.ql = org.spark-project.hive:hive-exec:1.2.1.spark2
* parquet.hadoop = com.twitter:parquet-hadoop-bundle:1.6.0
---
---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
