Add tests and Cargo fmt

vortex-file/src/v2/exec/mod.rs

@@ -7,6 +7,14 @@ use vortex_array::ArrayData;
 use vortex_error::VortexResult;
 
 /// An execution driver is used to drive the execution of the scan operation.
+///
+/// It is passed a stream of futures that (typically) process a single split of the file.
+/// Drivers are able to control the concurrency of the execution with [`futures::stream::buffered`],
+/// as well as _where_ the futures are executed by spawning them onto a specific runtime or thread
+/// pool.
+///
+/// Note that the futures encapsulate heavy CPU code such as filtering and decompression. To
+/// offload keep I/O work separate, please see the [`crate::v2::io::IoDriver`] trait.
 pub trait ExecDriver {
     fn drive(
         &self,

vortex-file/src/v2/io/mod.rs

@@ -9,7 +9,11 @@ use crate::v2::segments::SegmentRequest;
 ///
 /// Each request contains a [`vortex_layout::segments::SegmentId`] as well as a one-shot callback
 /// channel to post back the result.
+///
+/// I/O drivers are able to coalesce, debounce, or otherwise group the requests, as well as control the concurrency
+/// of the I/O operations with [`futures::stream::buffered`].
 pub trait IoDriver: 'static {
+    // NOTE(ngates): this isn't an async_trait since it doesn't need to be object-safe or boxed.
     fn drive(
         &self,
         stream: impl Stream<Item = SegmentRequest> + 'static,

vortex-file/src/v2/mod.rs

@@ -1,7 +1,7 @@
 mod exec;
 mod file;
 mod footer;
-pub mod io;
+mod io;
 mod open;
 pub mod segments;
 mod strategy;

vortex-file/src/v2/open/mod.rs

@@ -41,6 +41,7 @@ pub struct VortexOpenOptions {
     split_by: SplitBy,
     segment_cache: Option<Arc<dyn SegmentCache>>,
     execution_mode: Option<ExecutionMode>,
+    // TODO(ngates): allow fully configurable I/O driver.
     io_concurrency: usize,
 }