etseidl commented on code in PR #8671:
URL: https://github.com/apache/arrow-rs/pull/8671#discussion_r2547720410
##########
parquet/src/file/metadata/memory.rs:
##########
@@ -50,9 +51,60 @@ impl<T: HeapSize> HeapSize for Vec<T> {
}
}
+impl<K: HeapSize, V: HeapSize> HeapSize for HashMap<K, V> {
+ fn heap_size(&self) -> usize {
+ let capacity = self.capacity();
+ if capacity == 0 {
+ return 0;
+ }
+
+ // HashMap doesn't provide a way to get its heap size, so this is an
approximation based on
+ // the behavior of hashbrown::HashMap as at version 0.16.0, and may
become inaccurate
+ // if the implementation changes.
+ let key_val_size = std::mem::size_of::<(K, V)>();
+ // Overhead for the control tags group, which may be smaller depending
on architecture
+ let group_size = 16;
+ // 1 byte of metadata stored per bucket.
+ let metadata_size = 1;
+
+ // Compute the number of buckets for the capacity. Based on
hashbrown's capacity_to_buckets
+ let buckets = if capacity < 15 {
+ let min_cap = match key_val_size {
+ 0..=1 => 14,
+ 2..=3 => 7,
+ _ => 3,
+ };
+ let cap = min_cap.max(capacity);
+ if cap < 4 {
+ 4
+ } else if cap < 8 {
+ 8
+ } else {
+ 16
+ }
+ } else {
+ (capacity.saturating_mul(8) / 7).next_power_of_two()
+ };
+
+ group_size
+ + (buckets * (key_val_size + metadata_size))
+ + self.keys().map(|k| k.heap_size()).sum::<usize>()
+ + self.values().map(|v| v.heap_size()).sum::<usize>()
+ }
+}
+
impl<T: HeapSize> HeapSize for Arc<T> {
fn heap_size(&self) -> usize {
- self.as_ref().heap_size()
+ // Arc stores weak and strong counts on the heap alongside an instance
of T
+ 2 * std::mem::size_of::<usize>() + std::mem::size_of::<T>() +
self.as_ref().heap_size()
Review Comment:
I think it's correct.
```rust
let v = Vec::<i32>::new();
println!("empty vec heap size {}", v.heap_size());
println!("size of vec {}", std::mem::size_of::<Vec<i32>>());
let av = Arc::new(v);
println!("arc<vec> heap size {}", av.heap_size());
```
prints
```
empty vec heap size 0
size of vec 24
arc<vec> heap size 40
```
filling `v` with 20 values
```
filled vec heap size 80
size of vec 24
arc<vec> heap size 120
```
Assuming `Arc` adds the 2 `usize`, this looks correct to me.
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