2010YOUY01 commented on code in PR #21821:
URL: https://github.com/apache/datafusion/pull/21821#discussion_r3198520758
##########
benchmarks/src/hj.rs:
##########
@@ -303,6 +301,86 @@ const HASH_QUERIES: &[HashJoinQuery] = &[
build_size: "100K_(20%_dups)",
probe_size: "60M",
},
+ // RightSemi Join benchmarks with Int32 keys
+ // Q16: RightSemi, Small build (25 rows), 100% Hit rate
Review Comment:
Hmm, my previous explanation may have been confusing. Let me try again.
Suppose we have the query:
```sql
SELECT *
FROM generate_series(100) AS t1(v1)
RIGHT SEMI JOIN generate_series(10) AS t2(v1)
ON (t1.v1 % 10) = t2.v1
```
Here, each probe row from `t2` matches 10 rows on average from `t1`, so the
matching rows per probe row ratio is `10:1`.
Although a semi join only returns whether a match exists, this ratio still
matters for execution behavior, because we are evaluating short-circuit
optimizations here.
So I suggest we could doc this metric here. See the original reply for how
to get this matching ratio metric automatically.
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