scovich commented on code in PR #9117: URL: https://github.com/apache/arrow-rs/pull/9117#discussion_r2678961525
########## 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: nit: I know this is how the row index reader did it, but since that code merged I learned that [Iterator::by_ref](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.by_ref) is a thing. ```suggestion .extend(self.remaining_indices.by_ref().take(batch_size)); ``` It's not shorter, but does seem more readable? (more below) ########## parquet/src/arrow/schema/virtual_type.rs: ########## @@ -27,6 +27,50 @@ macro_rules! VIRTUAL_PREFIX { }; } +/// The extension type for row group indices +/// +/// Extension name: `parquet.virtual.row_group_index` +/// +/// This virtual column has storage type `Int64` and uses empty string metadata +#[derive(Debug, Default, Clone, Copy, PartialEq)] +pub struct RowGroupIndex; + +impl ExtensionType for RowGroupIndex { + const NAME: &'static str = concat!(VIRTUAL_PREFIX!(), "row_group_index"); + type Metadata = &'static str; + + fn metadata(&self) -> &Self::Metadata { + &"" + } + + fn serialize_metadata(&self) -> Option<String> { + Some(String::default()) + } + + fn deserialize_metadata(metadata: Option<&str>) -> Result<Self::Metadata, ArrowError> { + if metadata.is_some_and(str::is_empty) { + Ok("") + } else { + Err(ArrowError::InvalidArgumentError( + "Virtual column extension type expects an empty string as metadata".to_owned(), + )) + } Review Comment: nit: is a match simpler? ```suggestion match metadata { Some(&"") => Ok(""), _ => Err(ArrowError::InvalidArgumentError( "Virtual column extension type expects an empty string as metadata".to_owned(), )), } ``` or even ```suggestion if let Some(&"") = metadata { return Ok(""); }; Err(ArrowError::InvalidArgumentError( "Virtual column extension type expects an empty string as metadata".to_owned(), )) ``` ########## 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 Review Comment: nit: I would expect m < n, so this is O(n) where n is the total row groups, and the loop below is O(m) where m is the number of selected row groups? -- This is an automated message from the Apache Git Service. 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