[GitHub] [arrow-rs] crepererum commented on a change in pull request #307: ensure null-counts are written for all-null columns

[GitBox]

crepererum commented on a change in pull request #307:
URL: https://github.com/apache/arrow-rs/pull/307#discussion_r635925090



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File path: parquet/src/column/writer.rs
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@@ -607,9 +607,11 @@ impl<T: DataType> ColumnWriterImpl<T> {
         let max_def_level = self.descr.max_def_level();
         let max_rep_level = self.descr.max_rep_level();
 
+        // always update column NULL count, no matter if page stats are used
+        self.num_column_nulls += self.num_page_nulls;

Review comment:
       There are two variables here: `num_page_nulls` (which IS updated) and 
`num_column_nulls` (which prior to this PR was only updated if min/max values 
were set, which cannot happen for all-NULL columns). And the latter one 
(`num_column_nulls`) will be used to write the stats.




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