etseidl commented on code in PR #9700:
URL: https://github.com/apache/arrow-rs/pull/9700#discussion_r3080951829
##########
parquet/src/arrow/arrow_writer/mod.rs:
##########
@@ -4827,6 +4895,48 @@ mod tests {
assert_eq!(get_dict_page_size(col1_meta), 1024 * 1024 * 4);
}
+ #[test]
+ fn test_dict_page_size_decided_by_compression_fallback() {
Review Comment:
As a test, I saved the output from this and examined the sizing. Without the
heuristic, the encoded size for col0 is 8658384 bytes (the default fallback
mechanism kicked in after 7 pages). With the heuristic, col1 is 8391126 bytes,
a savings of 3%.
I also modified the test to mod the index with 32767. In that instance, col1
was still 8391126 bytes, but col0 was only 2231581, nearly 4X smaller.
I know this is not entirely representative, but it does again point out the
pitfalls of too simplistic an approach.
##########
parquet/src/column/writer/encoder.rs:
##########
@@ -109,6 +109,12 @@ pub trait ColumnValueEncoder {
/// <already_written_encoded_byte_size> +
<estimated_encoded_size_of_unflushed_bytes>
fn estimated_data_page_size(&self) -> usize;
+ /// Returns the estimated size of plainly encoded data, in bytes,
+ /// that would be written without a dictionary.
+ /// If there is no dictionary, or the data size statistic is not available,
+ /// returns `None`.
+ fn uncompressed_data_size(&self) -> Option<usize>;
Review Comment:
To avoid confusion I'd prefer this be named `plain_encoded_data_size` or
some such. To me, compression is performed on the page after encoding.
##########
parquet/src/encodings/encoding/plain_counter.rs:
##########
@@ -0,0 +1,75 @@
+// 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::basic::Type;
+use crate::data_type::private::ParquetValueType;
+use crate::schema::types::ColumnDescriptor;
+
+/// A helper to estimate the size of plain encoding of the values
+/// that were written to the dictionary encoder.
+///
+/// This is used to enhance the dictionary fallback heuristic with the logic
+/// that the writer should fall back to the plain encoding when at a certain
point,
+/// e.g. after encoding the first batch, the total size of unencoded data
+/// is calculated as smaller than `(encodedSize + dictionarySize)`.
+pub struct PlainDataSizeCounter {
Review Comment:
To my comment about sample size, perhaps this can be adapted to keep track
of both the plain and dictionary encoded sizes, and then only make a decision
after some critical number of rows or bytes have been processed.
##########
parquet/src/data_type.rs:
##########
@@ -1071,9 +1081,8 @@ pub(crate) mod private {
Ok(num_values)
}
- #[inline]
- fn dict_encoding_size(&self) -> (usize, usize) {
- (std::mem::size_of::<u32>(), self.len())
+ fn dict_encoding_size(&self) -> usize {
+ 4 + self.len()
}
Review Comment:
To be fair, there's magic all over this module. But I agree with @EmilyMatt
there's no need to add more.
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