friendlymatthew commented on code in PR #9117: URL: https://github.com/apache/arrow-rs/pull/9117#discussion_r2688357489
########## parquet/src/arrow/array_reader/row_group_index.rs: ########## @@ -0,0 +1,214 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +use crate::arrow::array_reader::ArrayReader; +use crate::errors::{ParquetError, Result}; +use crate::file::metadata::{ParquetMetaData, RowGroupMetaData}; +use arrow_array::{ArrayRef, Int64Array}; +use arrow_schema::DataType; +use std::any::Any; +use std::collections::HashMap; +use std::sync::Arc; + +pub(crate) struct RowGroupIndexReader { + buffered_indices: Vec<i64>, + remaining_indices: std::iter::Flatten<std::vec::IntoIter<std::iter::RepeatN<i64>>>, +} + +impl RowGroupIndexReader { + pub(crate) fn try_new<'a>( + parquet_metadata: &'a ParquetMetaData, + row_groups: impl Iterator<Item = &'a RowGroupMetaData>, + ) -> Result<Self> { + // build mapping from ordinal to row group index + // this is O(M) where M is the total number of row groups in the file + let ordinal_to_index: HashMap<i16, i64> = + HashMap::from_iter(parquet_metadata.row_groups().iter().enumerate().filter_map( + |(row_group_index, rg)| { + rg.ordinal() + .map(|ordinal| (ordinal, row_group_index as i64)) + }, + )); + + // build repeating iterators in the order specified by the row_groups iterator + // this is O(n) where n is the number of selected row groups + let repeated_indices: Vec<_> = row_groups + .map(|rg| { + let ordinal = rg.ordinal().ok_or_else(|| { + ParquetError::General( + "Row group missing ordinal field, required to compute row group indices" + .to_string(), + ) + })?; + + let row_group_index = ordinal_to_index.get(&ordinal).ok_or_else(|| { + ParquetError::General(format!( + "Row group with ordinal {} not found in metadata", + ordinal + )) + })?; + + // repeat row group index for each row in this row group + Ok(std::iter::repeat_n( + *row_group_index, + rg.num_rows() as usize, + )) + }) + .collect::<Result<_>>()?; + + Ok(Self { + buffered_indices: Vec::new(), + remaining_indices: repeated_indices.into_iter().flatten(), + }) + } +} + +impl ArrayReader for RowGroupIndexReader { + fn read_records(&mut self, batch_size: usize) -> Result<usize> { + let starting_len = self.buffered_indices.len(); + self.buffered_indices + .extend((&mut self.remaining_indices).take(batch_size)); Review Comment: TIL. Thank you @scovich -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
