Rachelint commented on code in PR #15591:
URL: https://github.com/apache/datafusion/pull/15591#discussion_r2072417977
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datafusion/expr-common/src/groups_accumulator.rs:
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@@ -250,4 +288,30 @@ pub trait GroupsAccumulator: Send {
/// This function is called once per batch, so it should be `O(n)` to
/// compute, not `O(num_groups)`
fn size(&self) -> usize;
+
+ /// Returns `true` if this accumulator supports blocked groups.
+ fn supports_blocked_groups(&self) -> bool {
+ false
+ }
+
+ /// Alter the block size in the accumulator
+ ///
+ /// If the target block size is `None`, it will use a single big
+ /// block(can think it a `Vec`) to manage the state.
+ ///
+ /// If the target block size` is `Some(blk_size)`, it will try to
+ /// set the block size to `blk_size`, and the try will only success
+ /// when the accumulator has supported blocked mode.
+ ///
+ /// NOTICE: After altering block size, all data in previous will be
cleared.
Review Comment:
Yes, it will be usually used in `load back + merge` step in spilling:
- Emit the rest blocks at first
- Then switch to `flat mode` and perform sorted aggregation
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