joshrosen-stripe commented on a change in pull request #26993:
[WIP][SPARK-30338][SQL] Avoid unnecessary InternalRow copies in
ParquetRowConverter
URL: https://github.com/apache/spark/pull/26993#discussion_r361050050
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetRowConverter.scala
##########
@@ -318,10 +318,31 @@ private[parquet] class ParquetRowConverter(
new ParquetMapConverter(parquetType.asGroupType(), t, updater)
case t: StructType =>
+ val wrappedUpdater = {
+ if (updater.isInstanceOf[RowUpdater]) {
+ // `updater` is a RowUpdater, implying that the parent container
is a struct.
+ // We do NOT need to perform defensive copying here because either:
+ //
+ // 1. The path from the schema root to this field consists only
of nested
+ // structs, so this converter will only be invoked once per
record and
+ // we don't need to copy because copying will be done in the
final
+ // UnsafeProjection, or
+ // 2. The path from the schema root to this field contains a map
or array,
+ // in which case we will perform a recursive defensive copy
via the
Review comment:
Correctness relies on the copy actually being a deep copy. Looking elsewhere
in this file, we have comments like
```
// NOTE: We can't reuse the mutable Map here and must instantiate a new
`Map` for the next
// value. `Row.copy()` only copies row cells, it doesn't do deep copy
to objects stored in row
// cells.
```
which suggest that certain copying might be shallow, so it's important to
double-check and make sure that the copies are indeed deep.
Here, the state being copied is an `InternalRow`. To be more specific, it's
actually a `SpecificInternalRow` (I'll update the `.asInstanceOf` cast below to
reflect this). `SpecificInternalRow` extends `BaseGenericInternalRow` and
#18483 changed that to implement a deep-copy, recursively copying maps, arrays,
and structs.
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