Add pcodec 1k-page-size benchmark

Adds a divan benchmark that compares pcodec with the default page size
against pcodec configured with a 1024-value page size on f64 and i64
data. The bench reports the compression ratio of each variant on
startup and times compression, full decompression, and per-element
scalar_at access for both, so we can quantify the size/random-access
tradeoff of smaller pco pages.

Signed-off-by: Claude <noreply@anthropic.com>

Author: claude

vortex/Cargo.toml

@@ -102,3 +102,8 @@ test = false
 [[bench]]
 name = "pipeline"
 harness = false
+
+[[bench]]
+name = "pcodec_page_size"
+harness = false
+test = false

vortex/benches/pcodec_page_size.rs

@@ -0,0 +1,260 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright the Vortex contributors
+
+//! Compare pcodec with the default page size against pcodec with a 1024-value
+//! ("1k") page size on `f64` and `i64` data.
+//!
+//! Pcodec lets you tune the page size independently of the chunk size. Smaller
+//! pages add per-page overhead (so the compression ratio gets worse) but let
+//! random access decode a much smaller window, which should help `scalar_at`.
+//! These benches measure both effects.
+
+#![expect(clippy::unwrap_used)]
+#![expect(clippy::cast_precision_loss)]
+
+use std::sync::LazyLock;
+
+use divan::Bencher;
+#[cfg(not(codspeed))]
+use divan::counter::BytesCount;
+use mimalloc::MiMalloc;
+use rand::RngExt;
+use rand::SeedableRng;
+use rand::rngs::StdRng;
+use vortex::array::IntoArray;
+use vortex::array::LEGACY_SESSION;
+use vortex::array::VortexSessionExecute;
+use vortex::array::arrays::PrimitiveArray;
+use vortex::array::session::ArraySession;
+use vortex::encodings::pco::Pco;
+use vortex::encodings::pco::PcoArray;
+use vortex_session::VortexSession;
+
+#[global_allocator]
+static GLOBAL: MiMalloc = MiMalloc;
+
+static SESSION: LazyLock<VortexSession> =
+    LazyLock::new(|| VortexSession::empty().with::<ArraySession>());
+
+const NUM_VALUES: usize = 100_000;
+const NUM_ACCESSES: usize = 1000;
+
+/// `0` tells `Pco::from_primitive` to fall back to the chunk-default page size
+/// (`pco::DEFAULT_MAX_PAGE_N`, currently 262144 values).
+const DEFAULT_PAGE: usize = 0;
+const PAGE_1K: usize = 1024;
+const COMPRESSION_LEVEL: usize = 3;
+
+fn setup_arrays() -> (PrimitiveArray, PrimitiveArray) {
+    let mut rng = StdRng::seed_from_u64(0);
+    // A noisy ramp: large dynamic range with smooth structure - the kind of
+    // data where pcodec's bin/offset scheme actually does work, so the page
+    // overhead is visible in the compression ratio.
+    let f64_array = PrimitiveArray::from_iter((0..NUM_VALUES).map(|i| {
+        let noise: f64 = rng.random_range(-0.5..0.5);
+        i as f64 * 0.001 + noise
+    }));
+    let i64_array =
+        PrimitiveArray::from_iter((0..NUM_VALUES).map(|i| i as i64 + rng.random_range(-50..50)));
+    (f64_array, i64_array)
+}
+
+fn compress(parray: &PrimitiveArray, values_per_page: usize) -> PcoArray {
+    let mut ctx = SESSION.create_execution_ctx();
+    Pco::from_primitive(
+        parray.as_view(),
+        COMPRESSION_LEVEL,
+        values_per_page,
+        &mut ctx,
+    )
+    .unwrap()
+}
+
+fn print_compression_ratios() {
+    let (f64_array, i64_array) = setup_arrays();
+    let f64_uncompressed = f64_array.nbytes();
+    let i64_uncompressed = i64_array.nbytes();
+
+    let f64_default = compress(&f64_array, DEFAULT_PAGE).nbytes();
+    let f64_1k = compress(&f64_array, PAGE_1K).nbytes();
+    let i64_default = compress(&i64_array, DEFAULT_PAGE).nbytes();
+    let i64_1k = compress(&i64_array, PAGE_1K).nbytes();
+
+    eprintln!();
+    eprintln!(
+        "pcodec page-size compression ratio ({NUM_VALUES} values, level {COMPRESSION_LEVEL}):"
+    );
+    eprintln!("  f64  uncompressed = {:>10} bytes", f64_uncompressed);
+    eprintln!(
+        "  f64  default page = {:>10} bytes  ({:.3}x, {:.2} bits/value)",
+        f64_default,
+        f64_uncompressed as f64 / f64_default as f64,
+        (f64_default as f64 * 8.0) / NUM_VALUES as f64,
+    );
+    eprintln!(
+        "  f64  1k      page = {:>10} bytes  ({:.3}x, {:.2} bits/value)",
+        f64_1k,
+        f64_uncompressed as f64 / f64_1k as f64,
+        (f64_1k as f64 * 8.0) / NUM_VALUES as f64,
+    );
+    eprintln!("  i64  uncompressed = {:>10} bytes", i64_uncompressed);
+    eprintln!(
+        "  i64  default page = {:>10} bytes  ({:.3}x, {:.2} bits/value)",
+        i64_default,
+        i64_uncompressed as f64 / i64_default as f64,
+        (i64_default as f64 * 8.0) / NUM_VALUES as f64,
+    );
+    eprintln!(
+        "  i64  1k      page = {:>10} bytes  ({:.3}x, {:.2} bits/value)",
+        i64_1k,
+        i64_uncompressed as f64 / i64_1k as f64,
+        (i64_1k as f64 * 8.0) / NUM_VALUES as f64,
+    );
+    eprintln!();
+}
+
+fn with_byte_counter<'a, 'b>(bencher: Bencher<'a, 'b>, bytes: u64) -> Bencher<'a, 'b> {
+    #[cfg(not(codspeed))]
+    return bencher.counter(BytesCount::new(bytes));
+    #[cfg(codspeed)]
+    {
+        _ = bytes;
+        return bencher;
+    }
+}
+
+fn random_indices() -> Vec<usize> {
+    let mut rng = StdRng::seed_from_u64(1);
+    (0..NUM_ACCESSES)
+        .map(|_| rng.random_range(0..NUM_VALUES))
+        .collect()
+}
+
+fn main() {
+    print_compression_ratios();
+    divan::main();
+}
+
+// --- compression ---
+
+#[divan::bench(name = "pcodec_compress_f64_default_page")]
+fn bench_compress_f64_default(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&f64_array, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| {
+            Pco::from_primitive(a.as_view(), COMPRESSION_LEVEL, DEFAULT_PAGE, ctx).unwrap()
+        });
+}
+
+#[divan::bench(name = "pcodec_compress_f64_1k_page")]
+fn bench_compress_f64_1k(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&f64_array, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| {
+            Pco::from_primitive(a.as_view(), COMPRESSION_LEVEL, PAGE_1K, ctx).unwrap()
+        });
+}
+
+#[divan::bench(name = "pcodec_compress_i64_default_page")]
+fn bench_compress_i64_default(bencher: Bencher) {
+    let (_, i64_array) = setup_arrays();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&i64_array, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| {
+            Pco::from_primitive(a.as_view(), COMPRESSION_LEVEL, DEFAULT_PAGE, ctx).unwrap()
+        });
+}
+
+#[divan::bench(name = "pcodec_compress_i64_1k_page")]
+fn bench_compress_i64_1k(bencher: Bencher) {
+    let (_, i64_array) = setup_arrays();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&i64_array, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| {
+            Pco::from_primitive(a.as_view(), COMPRESSION_LEVEL, PAGE_1K, ctx).unwrap()
+        });
+}
+
+// --- decompression (full) ---
+
+#[divan::bench(name = "pcodec_decompress_f64_default_page")]
+fn bench_decompress_f64_default(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    let compressed = compress(&f64_array, DEFAULT_PAGE).into_array();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&compressed, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| (**a).clone().execute::<PrimitiveArray>(ctx).unwrap());
+}
+
+#[divan::bench(name = "pcodec_decompress_f64_1k_page")]
+fn bench_decompress_f64_1k(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    let compressed = compress(&f64_array, PAGE_1K).into_array();
+    with_byte_counter(bencher, (NUM_VALUES * 8) as u64)
+        .with_inputs(|| (&compressed, SESSION.create_execution_ctx()))
+        .bench_refs(|(a, ctx)| (**a).clone().execute::<PrimitiveArray>(ctx).unwrap());
+}
+
+// --- scalar_at ---
+
+#[divan::bench(name = "pcodec_scalar_at_f64_default_page")]
+fn bench_scalar_at_f64_default(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    let compressed = compress(&f64_array, DEFAULT_PAGE).into_array();
+    let indices = random_indices();
+    bencher
+        .with_inputs(|| (&compressed, &indices))
+        .bench_refs(|(array, indices)| {
+            let mut ctx = LEGACY_SESSION.create_execution_ctx();
+            for &idx in indices.iter() {
+                divan::black_box(array.execute_scalar(idx, &mut ctx).unwrap());
+            }
+        });
+}
+
+#[divan::bench(name = "pcodec_scalar_at_f64_1k_page")]
+fn bench_scalar_at_f64_1k(bencher: Bencher) {
+    let (f64_array, _) = setup_arrays();
+    let compressed = compress(&f64_array, PAGE_1K).into_array();
+    let indices = random_indices();
+    bencher
+        .with_inputs(|| (&compressed, &indices))
+        .bench_refs(|(array, indices)| {
+            let mut ctx = LEGACY_SESSION.create_execution_ctx();
+            for &idx in indices.iter() {
+                divan::black_box(array.execute_scalar(idx, &mut ctx).unwrap());
+            }
+        });
+}
+
+#[divan::bench(name = "pcodec_scalar_at_i64_default_page")]
+fn bench_scalar_at_i64_default(bencher: Bencher) {
+    let (_, i64_array) = setup_arrays();
+    let compressed = compress(&i64_array, DEFAULT_PAGE).into_array();
+    let indices = random_indices();
+    bencher
+        .with_inputs(|| (&compressed, &indices))
+        .bench_refs(|(array, indices)| {
+            let mut ctx = LEGACY_SESSION.create_execution_ctx();
+            for &idx in indices.iter() {
+                divan::black_box(array.execute_scalar(idx, &mut ctx).unwrap());
+            }
+        });
+}
+
+#[divan::bench(name = "pcodec_scalar_at_i64_1k_page")]
+fn bench_scalar_at_i64_1k(bencher: Bencher) {
+    let (_, i64_array) = setup_arrays();
+    let compressed = compress(&i64_array, PAGE_1K).into_array();
+    let indices = random_indices();
+    bencher
+        .with_inputs(|| (&compressed, &indices))
+        .bench_refs(|(array, indices)| {
+            let mut ctx = LEGACY_SESSION.create_execution_ctx();
+            for &idx in indices.iter() {
+                divan::black_box(array.execute_scalar(idx, &mut ctx).unwrap());
+            }
+        });
+}