hudi hard deletion in flink sql AND detect deletions of upstream

[vtygoss]

Hi, 


I have two problems:


1. How to specify hard deletion in hudi-flink-bundle-0.9.0? 
2. How to detect the deletion events in downstream hudi-flink sql streaming?  
The down streams need to detect the deletions of input hudi table and act 
accordingly.




I tried to use org.apache.hudi.common.model. EmptyHoodieRecordPayload, but it 
seems like that EmptyHoodieRecordPayload is not really deletion but emits null 
value of none primary key? i am not sure.  BTW, klass EmptyHoodieRecordPayload 
is lack of a constructor of parameter klass 
“org.apache.hudi.common.util.Option". 


please offer some advices, thank you very much!


Best Regards!




```
CREATE TABLE t3(
  uuid VARCHAR(20), 
  name VARCHAR(10),
  age INT,
  ts TIMESTAMP(3),
  `partition` VARCHAR(20),
  primary key(uuid) not enforced
)
PARTITIONED BY (`partition`)
WITH (
  'connector' = 'hudi',
  'path' = 'hdfs://bruneihealth/user/data/db/hudi_flink/t3',
  'table.type' = 'MERGE_ON_READ',
  'read.tasks' = '1',
  'read.streaming.enabled' = 'true',  
  'read.streaming.check-interval' = '1', 
  'hoodie.datasource.write.partitionpath.field'='_hoodie_partition_path',
  'write.payload.class' = 
'org.apache.hudi.common.model.EmptyHoodieRecordPayload',
  'compaction.async.enabled'='false'
);
```