test: expose internals for benchmarking

This commit is a bit of a hack. The first thing I could think of. The
problem is that I want to be able to benchmark various modules in the
read buffer but I don't want to expose those internals via the external
API.

Becuase criterion only lets you exercise the exported API I needed to
expose some internals. I did this by creating a documented module
`benchmarks` in the `read_buffer` crate, which re-exports identifiers
that can be used by a criterion crate.

The idea is that it will be clear that this module is not part of the
public API.

read_buffer/benches/dictionary.rs

@@ -3,7 +3,7 @@ use rand::distributions::Alphanumeric;
 use rand::prelude::*;
 use rand::Rng;
 
-use read_buffer::{column::cmp::Operator, column::dictionary, column::RowIDs};
+use read_buffer::benchmarks::{dictionary, Operator, RowIDs};
 
 const ROWS: [usize; 3] = [100_000, 1_000_000, 10_000_000];
 const LOCATIONS: [Location; 3] = [Location::Start, Location::Middle, Location::End];

read_buffer/benches/fixed.rs

@@ -4,8 +4,8 @@ use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Through
 use rand::prelude::*;
 
 use arrow_deps::arrow::datatypes::*;
-use read_buffer::column::fixed::Fixed;
-use read_buffer::column::fixed_null::FixedNull;
+use read_buffer::benchmarks::Fixed;
+use read_buffer::benchmarks::FixedNull;
 
 const ROWS: [usize; 5] = [10, 100, 1_000, 10_000, 60_000];
 const CHUNKS: [Chunks; 4] = [

read_buffer/benches/plain.rs

@@ -4,8 +4,8 @@ use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Through
 use rand::prelude::*;
 
 use arrow_deps::arrow::datatypes::*;
-use read_buffer::column::fixed::Fixed;
-use read_buffer::column::fixed_null::FixedNull;
+use read_buffer::benchmarks::Fixed;
+use read_buffer::benchmarks::FixedNull;
 
 const ROWS: [usize; 5] = [10, 100, 1_000, 10_000, 60_000];
 const CHUNKS: [Chunks; 4] = [

read_buffer/benches/row_group.rs

@@ -7,9 +7,8 @@ use rand::Rng;
 use rand_distr::{Distribution, Normal};
 
 use packers::{sorter, Packers};
-
-use read_buffer::column::{AggregateType, Column};
-use read_buffer::row_group::{ColumnType, Predicate, RowGroup};
+use read_buffer::benchmarks::{Column, ColumnType, RowGroup};
+use read_buffer::{AggregateType, Predicate};
 
 const ONE_MS: i64 = 1_000_000;
 

read_buffer/src/lib.rs

@@ -1017,3 +1017,17 @@ mod test {
         assert!(itr.next().is_none());
     }
 }
+
+/// THIS MODULE SHOULD ONLY BE IMPORTED FOR BENCHMARKS.
+///
+/// This module lets us expose internal parts of the crate so that we can use
+/// libraries like criterion for benchmarking.
+///
+/// It should not be imported into any non-testing or benchmarking crates.
+pub mod benchmarks {
+    pub use crate::column::{
+        cmp::Operator, dictionary, fixed::Fixed, fixed_null::FixedNull, Column, RowIDs,
+    };
+
+    pub use crate::row_group::{ColumnType, RowGroup};
+}