Make sure Arrow filter and take kernels early out where it makes …

…sense (#7704)

As expected, `take` didn't.

Before:

![image](https://github.com/user-attachments/assets/563067b6-53c0-4828-aaf6-b830f9ea3fcc)

After:

![image](https://github.com/user-attachments/assets/1307d019-aa0b-4135-a6a4-8452f8569aa1)


* Fixes #7632

crates/store/re_chunk/src/util.rs

@@ -377,6 +377,28 @@ pub fn take_array<A: ArrowArray + Clone, O: arrow2::types::Index>(
         "index arrays with validity bits are technically valid, but generally a sign that something went wrong",
     );
 
+    if indices.len() == array.len() {
+        let indices = indices.values().as_slice();
+
+        let starts_at_zero = || indices[0] == O::zero();
+        let is_consecutive = || {
+            indices
+                .windows(2)
+                .all(|values| values[1] == values[0] + O::one())
+        };
+
+        if starts_at_zero() && is_consecutive() {
+            #[allow(clippy::unwrap_used)]
+            return array
+                .clone()
+                .as_any()
+                .downcast_ref::<A>()
+                // Unwrap: that's initial type that we got.
+                .unwrap()
+                .clone();
+        }
+    }
+
     #[allow(clippy::unwrap_used)]
     arrow2::compute::take::take(array, indices)
         // Unwrap: this literally cannot fail.

crates/store/re_chunk/tests/memory_test.rs

@@ -61,7 +61,7 @@ use arrow2::{
     },
     offset::Offsets as ArrowOffsets,
 };
-use itertools::Itertools as _;
+use itertools::Itertools;
 
 #[test]
 fn filter_does_allocate() {
@@ -125,6 +125,72 @@ fn filter_does_allocate() {
     }
 }
 
+#[test]
+fn filter_empty_or_full_is_noop() {
+    re_log::setup_logging();
+
+    const NUM_SCALARS: i64 = 10_000_000;
+
+    let (((unfiltered, unfiltered_size_bytes), (filtered, filtered_size_bytes)), total_size_bytes) =
+        memory_use(|| {
+            let unfiltered = memory_use(|| {
+                let scalars = ArrowPrimitiveArray::from_vec((0..NUM_SCALARS).collect_vec());
+                ArrowListArray::<i32>::new(
+                    ArrowListArray::<i32>::default_datatype(scalars.data_type().clone()),
+                    ArrowOffsets::try_from_lengths(
+                        std::iter::repeat(NUM_SCALARS as usize / 10).take(10),
+                    )
+                    .unwrap()
+                    .into(),
+                    scalars.to_boxed(),
+                    None,
+                )
+            });
+
+            let filter = ArrowBooleanArray::from_slice(
+                std::iter::repeat(true)
+                    .take(unfiltered.0.len())
+                    .collect_vec(),
+            );
+            let filtered = memory_use(|| re_chunk::util::filter_array(&unfiltered.0, &filter));
+
+            (unfiltered, filtered)
+        });
+
+    eprintln!(
+        "unfiltered={} filtered={} total={}",
+        re_format::format_bytes(unfiltered_size_bytes as _),
+        re_format::format_bytes(filtered_size_bytes as _),
+        re_format::format_bytes(total_size_bytes as _),
+    );
+
+    assert!(
+        filtered_size_bytes < 1_000,
+        "filtered array should be the size of a few empty datastructures at most"
+    );
+
+    {
+        let unfiltered = unfiltered
+            .values()
+            .as_any()
+            .downcast_ref::<ArrowPrimitiveArray<i64>>()
+            .unwrap();
+        let filtered = filtered
+            .values()
+            .as_any()
+            .downcast_ref::<ArrowPrimitiveArray<i64>>()
+            .unwrap();
+
+        assert!(
+            std::ptr::eq(
+                unfiltered.values().as_ptr_range().start,
+                filtered.values().as_ptr_range().start
+            ),
+            "whole thing should be a noop -- pointers should match"
+        );
+    }
+}
+
 #[test]
 // TODO(cmc): That's the end goal, but it is simply impossible with `ListArray`'s encoding.
 //            See `Chunk::take_array`'s doc-comment for more information.
@@ -191,3 +257,65 @@ fn take_does_not_allocate() {
         );
     }
 }
+
+#[test]
+fn take_empty_or_full_is_noop() {
+    re_log::setup_logging();
+
+    const NUM_SCALARS: i64 = 10_000_000;
+
+    let (((untaken, untaken_size_bytes), (taken, taken_size_bytes)), total_size_bytes) =
+        memory_use(|| {
+            let untaken = memory_use(|| {
+                let scalars = ArrowPrimitiveArray::from_vec((0..NUM_SCALARS).collect_vec());
+                ArrowListArray::<i32>::new(
+                    ArrowListArray::<i32>::default_datatype(scalars.data_type().clone()),
+                    ArrowOffsets::try_from_lengths(
+                        std::iter::repeat(NUM_SCALARS as usize / 10).take(10),
+                    )
+                    .unwrap()
+                    .into(),
+                    scalars.to_boxed(),
+                    None,
+                )
+            });
+
+            let indices = ArrowPrimitiveArray::from_vec((0..untaken.0.len() as i32).collect_vec());
+            let taken = memory_use(|| re_chunk::util::take_array(&untaken.0, &indices));
+
+            (untaken, taken)
+        });
+
+    eprintln!(
+        "untaken={} taken={} total={}",
+        re_format::format_bytes(untaken_size_bytes as _),
+        re_format::format_bytes(taken_size_bytes as _),
+        re_format::format_bytes(total_size_bytes as _),
+    );
+
+    assert!(
+        taken_size_bytes < 1_000,
+        "taken array should be the size of a few empty datastructures at most"
+    );
+
+    {
+        let untaken = untaken
+            .values()
+            .as_any()
+            .downcast_ref::<ArrowPrimitiveArray<i64>>()
+            .unwrap();
+        let taken = taken
+            .values()
+            .as_any()
+            .downcast_ref::<ArrowPrimitiveArray<i64>>()
+            .unwrap();
+
+        assert!(
+            std::ptr::eq(
+                untaken.values().as_ptr_range().start,
+                taken.values().as_ptr_range().start
+            ),
+            "whole thing should be a noop -- pointers should match"
+        );
+    }
+}