Dongjoon Hyun created SPARK-23007:
-------------------------------------
Summary: Add schema evolution test suite
Key: SPARK-23007
URL: https://issues.apache.org/jira/browse/SPARK-23007
Project: Spark
Issue Type: Bug
Components: SQL, Tests
Affects Versions: 2.2.1
Reporter: Dongjoon Hyun
A schema can evolve in several ways and the followings are already supported in
file-based data sources.
1. Add a column
2. Remove a column
3. Change a column position
4. Change a column type
This issue aims to guarantee users a backward-compatible schema evolution
coverage on file-based data sources and to prevent future regressions by
*adding schema evolution test suites explicitly*.
Here, we consider safe evolution without data loss. For example, data type
evolution should be from small types to larger types like `int`-to-`long`, not
vice versa.
As of today, in the master branch, file-based data sources have schema
evolution coverages like the followings.
|| File Format || Coverage || Note
||
| TEXT | N/A | Schema consists of a single string column.
|
| CSV | 1, 2, 4 |
|
| JSON | 1, 2, 3, 4 |
|
| ORC | 1, 2, 3, 4 | Native vectorized ORC reader has the widest
coverage. |
| PARQUET | 1, 2, 3 |
|
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