kallisti-dev commented on code in PR #9058:
URL: https://github.com/apache/arrow-datafusion/pull/9058#discussion_r1470269524
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datafusion/execution/src/memory_pool/proxy.rs:
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@@ -36,24 +55,37 @@ pub trait VecAllocExt {
/// Note this calculation is not recursive, and does not include any heap
/// allocations contained within the Vec's elements. Does not include the
/// size of `self`
+ ///
+ /// # Example:
+ /// ```
+ /// # use datafusion_execution::memory_pool::proxy::VecAllocExt;
+ /// let mut vec = Vec::new();
+ /// // Push data into the vec and the accounting will be updated to reflect
+ /// // memory allocation
+ /// vec.push(1);
+ /// assert_eq!(vec.allocated_size(), 16); // space for 4 u32s
+ /// vec.push(1);
+ /// assert_eq!(vec.allocated_size(), 16); // no new allocation needed
+ ///
+ /// // push more data into the vec
+ /// for _ in 0..10 { vec.push(1); }
+ /// assert_eq!(vec.allocated_size(), 64); // space for 64 now
+ /// ```
fn allocated_size(&self) -> usize;
}
impl<T> VecAllocExt for Vec<T> {
type T = T;
fn push_accounted(&mut self, x: Self::T, accounting: &mut usize) {
- if self.capacity() == self.len() {
- // allocate more
-
- // growth factor: 2, but at least 2 elements
- let bump_elements = (self.capacity() * 2).max(2);
- let bump_size = std::mem::size_of::<u32>() * bump_elements;
- self.reserve(bump_elements);
+ let prev_capacty = self.capacity();
+ self.push(x);
+ let new_capacity = self.capacity();
+ if new_capacity > prev_capacty {
+ // capacity changed, so we allocated more
+ let bump_size = (new_capacity - prev_capacty) *
std::mem::size_of::<T>();
Review Comment:
thinking about it more: if `accounting` is tracking multiple vecs, then this
makes sense. multiplication should never overflow because `push` would panic
first in that case, but the `checked_add` could potentially overflow since
`accounting` could be some value greater than capacity.
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