Hi all:
i want to ask a question about broadcast nestloop join? from google i know,
that
left outer/semi join and right outer/semi join will use broadcast nestloop.
and in some cases, when the input data is very small, it is suitable to use.
so here
how to define the input data very small? what parameter decides the
threshold? I just want to disable it ( i found that set
spark.sql.autoBroadcastJoinThreshold= -1 is no work for sql:select a.key1 from
testdata1 as a where a.key1 not in (select key3 from testdata3) )
```
explain cost select a.key1 from testdata1 as a where a.key1 not in (select
key3 from testdata3);
== Physical Plan ==
*(1) Project [key1#90]
+- BroadcastNestedLoopJoin BuildRight, LeftAnti, ((key1#90 = key3#92) ||
isnull((key1#90 = key3#92)))
:- HiveTableScan [key1#90], HiveTableRelation `default`.`testdata1`,
org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [key1#90, value1#91]
+- BroadcastExchange IdentityBroadcastMode
+- HiveTableScan [key3#92], HiveTableRelation `default`.`testdata3`,
org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [key3#92, value3#93]
```
my question is
1. why in not in subquery , BroadcastNestedLoopJoin is still used even i set
spark.sql.autoBroadcastJoinThreshold= -1
2. which spark parameter decides enable/disable BroadcastNestedLoopJoin.
Appreciate if you have suggestion
Best Regards
Kelly Zhang
