aokolnychyi commented on code in PR #9050:
URL: https://github.com/apache/iceberg/pull/9050#discussion_r1393606348
##########
spark/v3.4/spark/src/main/java/org/apache/iceberg/spark/source/SparkWrite.java:
##########
@@ -390,7 +390,7 @@ private Expression conflictDetectionFilter() {
filter = Expressions.and(filter, expr);
}
- return filter;
+ return SERIALIZABLE == isolationLevel ? Expressions.alwaysTrue() :
filter;
Review Comment:
Here is the primary question. Are these statements equivalent?
```
MERGE INTO t USING (SELECT 1005 as id, 2 as class, SUM(value) as value FROM
t WHERE class = 1) AS u
ON t.id = u.id
WHEN MATCHED THEN UPDATE SET t.value = u.value
WHEN NOT MATCHED THEN INSERT (id, class, value) VALUES (u.id, u.class,
u.value)
```
```
MERGE INTO t USING (2 as class, SUM(value) as value FROM t WHERE class = 1)
AS u
ON t.id = 1005
WHEN MATCHED THEN UPDATE SET t.value = u.value
WHEN NOT MATCHED THEN INSERT (id, class, value) VALUES (1005, u.class,
u.value)
```
I think they would produce the same output, which probably makes them
logically equivalent. If they are equivalent, does it mean it is a valid
optimizer transform?
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