alamb commented on code in PR #6932:
URL: https://github.com/apache/arrow-datafusion/pull/6932#discussion_r1267837858
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datafusion/execution/src/memory_pool/mod.rs:
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@@ -221,6 +219,49 @@ pub fn human_readable_size(size: usize) -> String {
format!("{value:.1} {unit}")
}
+/// Tracks the change in memory to avoid overflow. Typically, this
+/// is isued like the following
+///
+/// 1. Call `delta.dec(sized_thing.size())`
+///
+/// 2. potentially change size of `sized_thing`
+///
+/// 3. Call `delta.inc(size_thing.size())`
+#[derive(Debug, Default)]
+pub struct MemoryDelta {
Review Comment:
The reason there was delta accounting is that in previous incarnations,
calculating the size for the overall grouping operator was a significant
bottleneck (for groupings with large cardinality groups) .
Specifically `Accumulator::size()` showed up on a bunch of perofiles.
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