Benchao Li created FLINK-18871:
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Summary: Non-deterministic function could break retract mechanism
Key: FLINK-18871
URL: https://issues.apache.org/jira/browse/FLINK-18871
Project: Flink
Issue Type: Bug
Components: Table SQL / API, Table SQL / Runtime
Reporter: Benchao Li
For example, we have a following SQL:
{code:sql}
create view view1 as
select
max(a) as m1,
max(b) as m2 -- b is a timestmap
from T
group by c, d;
create view view2 as
select * from view1
where m2 > CURRENT_TIMESTAMP;
insert into MySink
select sum(m1) as m1
from view2
group by c;
{code}
view1 will produce retract messages, and the same message in view2 maybe
produce different results. and the second agg will produce wrong result.
For example,
{noformat}
view1:
+ (1, 2020-8-10 16:13:00)
- (1, 2020-8-10 16:13:00)
+ (2, 2020-8-10 16:13:10)
view2:
+ (1, 2020-8-10 16:13:00)
- (1, 2020-8-10 16:13:00) // this record may be filtered out
+ (2, 2020-8-10 16:13:10)
MySink:
+ (1, 2020-8-10 16:13:00)
+ (2, 2020-8-10 16:13:10) // will produce wrong result.
{noformat}
In general, the non-deterministic function may break the retract mechanism. All
operators downstream which will rely on the retraction mechanism will produce
wrong results, or throw exception, such as Agg / some Sink which need retract
message / TopN / Window.
(The example above is a simplified version of some production jobs in our
scenario, just to explain the core problem)
CC [~ykt836] [~jark]
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