James Baker created SPARK-25943:
-----------------------------------
Summary: Corruption when writing data into a catalog table with a
different struct schema
Key: SPARK-25943
URL: https://issues.apache.org/jira/browse/SPARK-25943
Project: Spark
Issue Type: Bug
Components: Optimizer, SQL
Affects Versions: 2.3.2, 2.4.1, 2.5.0, 3.0.0
Reporter: James Baker
Suppose I have a catalog table with schema StructType(Seq(StructField("a",
StructType(Seq(StructField("b", DataTypes.StringType), StructField("c",
DataTypes.StringType))).
Suppose I now try to append a record to it:
{code:java}
{"a": {"c": "data1", "b": "data2"}}
{code}
That record will actually be appended as:
{code:java}
{"a": {"b": "data1", "c": "data2"}}
{code}
which is obviously not close to what the user wanted or expected (for me it
silently corrupted my data).
It turns out that the user could provide a totally different record,
{code:java}
{"a": {"this column": "is totally different", "but": "the types match up"}}
{code}
and it'd still get written out, but as
{code:java}
{"a": {"b": "is totally different", "c": "the types match up"}}
{code}
This is because [in
DDLPreprocessingUtils.castAndRenameOutput|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala#L500]
[,|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala#L500],]
and for DSV2 in [in
Analyzer.ResolveOutputRelation|https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala#L2239]
Spark puts effort in to reordering column names in line with what the output
expects, but merely casts any other types. This works nicely in a case where
you try to e.g. write an int into a double field, but goes wrong on complex
datatypes if the types match up but the field names do not.
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