GWphua commented on code in PR #18731:
URL: https://github.com/apache/druid/pull/18731#discussion_r2689571803
##########
processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/ByteBufferIntList.java:
##########
@@ -55,6 +55,7 @@ public void add(int val)
}
buffer.putInt(numElements * Integer.BYTES, val);
numElements++;
+ maxMergeBufferUsageBytes = Math.max(maxMergeBufferUsageBytes, numElements
* Integer.BYTES);
Review Comment:
I was thinking to get the maximum usage, because we request a
`getMergeBufferUsage` when `SpillingGrouper#close` is called. I do not really
know whether we are guaranteed to see the maximum usage when the grouper is
closing this class...
I am worried about the case where maybe we configure 1GiB to the merge
buffer, and the usage in the middle goes to, say 900MiB, but when the Grouper
is closed, the usage shows ~300MiB. The user is then encouraged to lower the
merge buffer allocation to 500MiB, which will be problematic.
This comment would also hopefully address your query about why `reset` does
not change `maxMergeBufferUsageBytes`.
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