wgtmac commented on code in PR #35989:
URL: https://github.com/apache/arrow/pull/35989#discussion_r1241374931
##########
cpp/src/parquet/statistics.cc:
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@@ -463,6 +463,8 @@ class TypedStatisticsImpl : public TypedStatistics<DType> {
public:
using T = typename DType::c_type;
+ // Currently, this constructor will tend to be called by ColumnWriter to
create the
Review Comment:
I still don't think comment with `currently` and `tend` is a good idea as it
may easily be out of sync and confuses users. It would be good enough to simply
describe its supposed use case.
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cpp/src/parquet/statistics.cc:
##########
@@ -543,7 +557,7 @@ class TypedStatisticsImpl : public TypedStatistics<DType> {
ResetCounts();
has_min_max_ = false;
has_distinct_count_ = false;
- has_null_count_ = false;
+ has_null_count_ = true;
Review Comment:
What about adding something like `ResetHasFlags()` below?
```cpp
void ResetHasFlags() {
has_min_max_ = false;
has_distinct_count_ = false;
has_null_count_ = true;
}
```
We can call it in the constructors and Reset() to make sure the initial
states are consistent.
##########
cpp/src/parquet/statistics.cc:
##########
@@ -552,12 +568,17 @@ class TypedStatisticsImpl : public TypedStatistics<DType>
{
void Merge(const TypedStatistics<DType>& other) override {
this->num_values_ += other.num_values();
+ // Merge always runs when Merge builder's page statistics
+ // into column chunk statistics, so it tent to have null count.
Review Comment:
```suggestion
// into column chunk statistics, so it tends to have null count.
```
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