[GitHub] [arrow-datafusion] viirya commented on a diff in pull request #7400: feat: Support spilling for hash aggregation

["viirya (via GitHub)" <gi...@apache.org>]

viirya commented on code in PR #7400:
URL: https://github.com/apache/arrow-datafusion/pull/7400#discussion_r1326437392


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datafusion/core/src/physical_plan/aggregates/row_hash.rs:
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@@ -120,6 +151,56 @@ use super::AggregateExec;
 /// hash table).
 ///
 /// [`group_values`]: Self::group_values
+///
+/// # Spilling
+///
+/// The sizes of group values and accumulators can become large. Before that causes out of memory,
+/// this hash aggregator outputs those data early for partial aggregation or spills to local disk
+/// using Arrow IPC format for final aggregation. For every input [`RecordBatch`], the memory
+/// manager checks whether the new input size meets the memory configuration. If not, outputting or
+/// spilling happens. For outputting, the final aggregation takes care of re-grouping. For spilling,

Review Comment:
   How does it decide to output or spill?



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