alamb commented on code in PR #5887:
URL: https://github.com/apache/arrow-rs/pull/5887#discussion_r1639079522
##########
parquet/src/arrow/arrow_reader/mod.rs:
##########
@@ -282,23 +284,41 @@ impl ArrowReaderOptions {
}
}
-/// The cheaply clone-able metadata necessary to construct a
[`ArrowReaderBuilder`]
+/// The metadata necessary to construct a [`ArrowReaderBuilder`]
///
-/// This allows loading the metadata for a file once and then using this to
construct
-/// multiple separate readers, for example, to distribute readers across
multiple threads
+/// Note this structure is cheaply clone-able as it consists of several arcs.
+///
+/// This structure allows
+///
+/// 1. Loading metadata for a file once and then using that same metadata to
+/// construct multiple separate readers, for example, to distribute readers
+/// across multiple threads
+///
+/// 2. Using a cached copy of the [`ParquetMetadata`] rather than reading it
Review Comment:
I also added the second and important usecase of not re-reading the metadata
on subsequent reads
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