[GitHub] [arrow] sunchao commented on a change in pull request #8525: ARROW-10387: [Rust][Parquet] Avoid call for file size metadata to read footer

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

sunchao commented on a change in pull request #8525:
URL: https://github.com/apache/arrow/pull/8525#discussion_r516152984



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File path: rust/parquet/src/file/footer.rs
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@@ -44,30 +44,31 @@ use crate::schema::types::{self, SchemaDescriptor};
 /// The reader first reads DEFAULT_FOOTER_SIZE bytes from the end of the file.
 /// If it is not enough according to the length indicated in the footer, it reads more bytes.
 pub fn parse_metadata<R: ChunkReader>(chunk_reader: &R) -> Result<ParquetMetaData> {
-    // check file is large enough to hold footer
-    let file_size = chunk_reader.len();
-    if file_size < (FOOTER_SIZE as u64) {
+    // read and cache up to DEFAULT_FOOTER_READ_SIZE bytes from the end and process the footer
+    let mut first_end_read = chunk_reader.get_read(

Review comment:
       yes exactly, I feel the footer reader should not be aware of how the input stream is processed and also the logic can vary depending on the remote storage so the `DEFAULT_FOOTER_READ_SIZE` may not fit for all.




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