alamb commented on code in PR #8694:
URL: https://github.com/apache/arrow-rs/pull/8694#discussion_r2498717158
##########
arrow-array/src/array/byte_view_array.rs:
##########
@@ -512,18 +512,71 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
};
}
- // 3) Allocate exactly capacity for all non-inline data
- let mut data_buf = Vec::with_capacity(total_large);
+ struct GcCopyGroup {
+ total_buffer_bytes: usize,
+ total_len: usize,
+ }
+
+ let mut groups = vec![];
+ let one_group = [GcCopyGroup {
+ total_buffer_bytes: total_large,
+ total_len: len,
+ }];
+ let gc_copy_groups = if total_large > i32::MAX as usize {
+ // Slow-path: need to split into multiple copy groups
+ let mut current_length = 0;
+ let mut current_elements = 0;
+
+ for view in self.views() {
+ let len = *view as u32;
+ if len > MAX_INLINE_VIEW_LEN {
+ if current_length + len > i32::MAX as u32 {
+ // Start a new group
+ groups.push(GcCopyGroup {
+ total_buffer_bytes: current_length as usize,
+ total_len: current_elements,
+ });
+ current_length = 0;
+ current_elements = 0;
+ }
+ current_length += len;
+ current_elements += 1;
+ }
+ }
+ if current_elements != 0 {
+ groups.push(GcCopyGroup {
+ total_buffer_bytes: current_length as usize,
+ total_len: current_elements,
+ });
+ }
+ &groups
+ } else {
+ one_group.as_slice()
+ };
+ debug_assert!(gc_copy_groups.len() <= i32::MAX as usize);
+
+ // 3) Copy the buffers group by group
+ let mut views_buf = Vec::with_capacity(len);
+ let mut data_blocks = Vec::with_capacity(gc_copy_groups.len());
+
+ let mut current_view_idx = 0;
+
+ for (group_idx, gc_copy_group) in gc_copy_groups.iter().enumerate() {
+ let mut data_buf =
Vec::with_capacity(gc_copy_group.total_buffer_bytes);
- // 4) Iterate over views and process each inline/non-inline view
- let views_buf: Vec<u128> = (0..len)
- .map(|i| unsafe { self.copy_view_to_buffer(i, &mut data_buf) })
- .collect();
+ // Directly push views to avoid intermediate Vec allocation
+ for view_idx in current_view_idx..current_view_idx +
gc_copy_group.total_len {
+ let view =
+ unsafe { self.copy_view_to_buffer(view_idx, group_idx as
i32, &mut data_buf) };
+ views_buf.push(view);
Review Comment:
However, since both `Vec`s are being modified at the same time, I couldn't
figure out a way to use `collect` here -- I could use extend
##########
arrow-array/src/array/byte_view_array.rs:
##########
@@ -512,18 +512,71 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
};
}
- // 3) Allocate exactly capacity for all non-inline data
- let mut data_buf = Vec::with_capacity(total_large);
+ struct GcCopyGroup {
+ total_buffer_bytes: usize,
+ total_len: usize,
+ }
+
+ let mut groups = vec![];
+ let one_group = [GcCopyGroup {
+ total_buffer_bytes: total_large,
+ total_len: len,
+ }];
+ let gc_copy_groups = if total_large > i32::MAX as usize {
+ // Slow-path: need to split into multiple copy groups
+ let mut current_length = 0;
+ let mut current_elements = 0;
+
+ for view in self.views() {
+ let len = *view as u32;
+ if len > MAX_INLINE_VIEW_LEN {
+ if current_length + len > i32::MAX as u32 {
+ // Start a new group
+ groups.push(GcCopyGroup {
+ total_buffer_bytes: current_length as usize,
+ total_len: current_elements,
+ });
+ current_length = 0;
+ current_elements = 0;
+ }
+ current_length += len;
+ current_elements += 1;
+ }
+ }
+ if current_elements != 0 {
+ groups.push(GcCopyGroup {
+ total_buffer_bytes: current_length as usize,
+ total_len: current_elements,
+ });
+ }
+ &groups
+ } else {
+ one_group.as_slice()
+ };
+ debug_assert!(gc_copy_groups.len() <= i32::MAX as usize);
+
+ // 3) Copy the buffers group by group
+ let mut views_buf = Vec::with_capacity(len);
+ let mut data_blocks = Vec::with_capacity(gc_copy_groups.len());
+
+ let mut current_view_idx = 0;
+
+ for (group_idx, gc_copy_group) in gc_copy_groups.iter().enumerate() {
+ let mut data_buf =
Vec::with_capacity(gc_copy_group.total_buffer_bytes);
- // 4) Iterate over views and process each inline/non-inline view
- let views_buf: Vec<u128> = (0..len)
- .map(|i| unsafe { self.copy_view_to_buffer(i, &mut data_buf) })
- .collect();
+ // Directly push views to avoid intermediate Vec allocation
+ for view_idx in current_view_idx..current_view_idx +
gc_copy_group.total_len {
+ let view =
+ unsafe { self.copy_view_to_buffer(view_idx, group_idx as
i32, &mut data_buf) };
+ views_buf.push(view);
Review Comment:
I think using collect doesn't allocate additional memory, but it can be
faster than `push` because `collect` does the capacity check once where `push`
has to check capacity on each call
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