[GitHub] [arrow] alamb commented on a change in pull request #9029: ARROW-10995: [Rust] [DataFusion] Limit ParquetExec concurrency when reading large number of files

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #9029:
URL: https://github.com/apache/arrow/pull/9029#discussion_r549472740



##########
File path: rust/datafusion/src/physical_plan/parquet.rs
##########
@@ -104,35 +105,41 @@ impl ParquetExec {
         filenames: &[&str],
         projection: Option<Vec<usize>>,
         batch_size: usize,
+        max_concurrency: usize,
     ) -> Result<Self> {
         // build a list of Parquet partitions with statistics and gather all unique schemas
         // used in this data set
         let mut schemas: Vec<Schema> = vec![];
-        let mut partitions = Vec::with_capacity(filenames.len());
-        for filename in filenames {
-            let file = File::open(filename)?;
-            let file_reader = Arc::new(SerializedFileReader::new(file)?);
-            let mut arrow_reader = ParquetFileArrowReader::new(file_reader);
-            let meta_data = arrow_reader.get_metadata();
-            // collect all the unique schemas in this data set
-            let schema = arrow_reader.get_schema()?;
-            if schemas.is_empty() || schema != schemas[0] {
-                schemas.push(schema);
-            }
-            let mut num_rows = 0;
-            let mut total_byte_size = 0;
-            for i in 0..meta_data.num_row_groups() {
-                let row_group_meta = meta_data.row_group(i);
-                num_rows += row_group_meta.num_rows();
-                total_byte_size += row_group_meta.total_byte_size();
+        let mut partitions = Vec::with_capacity(max_concurrency);
+        let filenames: Vec<String> = filenames.iter().map(|s| s.to_string()).collect();
+        let chunks = split_files(&filenames, max_concurrency);

Review comment:
       I suggest filing a follow on ticket to try and split work across `ColumnChunks` rather than files -- i think starting with just files is reasonable 




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org