Hi Etienne,
Very thanks for the article! Flink is currently indeed keeping increasing the
ability of unified batch / stream processing with the same api, and its a great
pleasure that more and more users are trying this functionality. But I also
have some questions regarding some details.
First IMO, as a whole for the long run Flink will have two unified APIs, namely
Table / SQL
API and DataStream API. Users could express the computation logic with these
two APIs
for both bounded and unbounded data processing. Underlying Flink provides two
execution modes: the streaming mode works with both bounded and unbounded data,
and it executes in a way of incremental processing based on state; the batch
mode works
only with bounded data, and it executes in a ways level-by-level similar to the
traditional
batch processing frameworks. Users could switch the execution mode via
EnvironmentSettings.inBatchMode() for
StreamExecutionEnvironment.setRuntimeMode().
Specially for DataStream, as implemented in FLIP-140, currently all the
existing DataStream
operation supports the batch execution mode in a unified way[1]: data will be
sorted for the
keyBy() edges according to the key, then the following operations like reduce()
could receive
all the data belonging to the same key consecutively, then it could directly
reducing the records
of the same key without maintaining the intermediate states. In this way users
could write the
same code for both streaming and batch processing with the same code.
# Regarding the migration of Join / Reduce
First I think Reduce is always supported and users could write
dataStream.keyBy().reduce(xx)
directly, and if batch execution mode is set, the reduce will not be executed
in a incremental way,
instead is acts much like sort-based aggregation in the traditional batch
processing framework.
Regarding Join, although the issue of FLINK-22587 indeed exists: current join
has to be bound
to a window and the GlobalWindow does not work properly, but with some more try
currently
it does not need users to re-write the whole join from scratch: Users could
write a dedicated
window assigner that assigns all the records to the same window instance and
return
EventTimeTrigger.create() as the default event-time trigger [2]. Then it works
source1.join(source2)
.where(a -> a.f0)
.equalTo(b -> b.f0)
.window(new EndOfStreamWindows())
.apply(xxxx);
It does not requires records have event-time attached since the trigger of
window is only
relying on the time range of the window and the assignment does not need
event-time either.
The behavior of the join is also similar to sort-based join if batch mode is
enabled.
Of course it is not easy to use to let users do the workaround and we'll try to
fix this issue in 1.17.
# Regarding support of Sort / Limit
Currently these two operators are indeed not supported in the DataStream API
directly. One initial
though for these two operations are that users may convert the DataStream to
Table API and use
Table API for these two operators:
DataStream<xx> xx = ... // Keeps the customized logic in DataStream
Table tableXX = tableEnv.fromDataStream(dataStream);
tableXX.orderBy($("a").asc());
How do you think about this option? We are also assessing if the combination of
DataStream
API / Table API is sufficient for all the batch users. Any suggestions are
warmly welcome.
Best,
Yun Gao
[1]
<https://cwiki.apache.org/confluence/display/FLINK/FLIP-140%3A+Introduce+batch-style+execution+for+bounded+keyed+streams
>https://nightlies.apache.org/flink/flink-docs-master/docs/dev/datastream/execution_mode/
<https://nightlies.apache.org/flink/flink-docs-master/docs/dev/datastream/execution_mode/
>
[2]
https://github.com/apache/flink-ml/blob/master/flink-ml-core/src/main/java/org/apache/flink/ml/common/datastream/EndOfStreamWindows.java
<https://github.com/apache/flink-ml/blob/master/flink-ml-core/src/main/java/org/apache/flink/ml/common/datastream/EndOfStreamWindows.java
>
------------------------------------------------------------------
From:liu ron <ron9....@gmail.com>
Send Time:2022 Nov. 8 (Tue.) 10:21
To:dev <d...@flink.apache.org>; Etienne Chauchot <echauc...@apache.org>; user
<user@flink.apache.org>
Subject:Re: [blog article] Howto migrate a real-life batch pipeline from the
DataSet API to the DataStream API
Thanks for your post, It looks very good to me, also maybe for developers,
Best,
Liudalong
yuxia <luoyu...@alumni.sjtu.edu.cn <mailto:luoyu...@alumni.sjtu.edu.cn >>
于2022年11月8日周二 09:11写道：
Wow, cool! Thanks for your work.
It'll be definitely helpful for the users that want to migrate their batch job
from DataSet API to DataStream API.
Best regards,
Yuxia
----- 原始邮件 -----
发件人: "Etienne Chauchot" <echauc...@apache.org <mailto:echauc...@apache.org >>
收件人: "dev" <d...@flink.apache.org <mailto:d...@flink.apache.org >>, "User"
<user@flink.apache.org <mailto:user@flink.apache.org >>
发送时间: 星期一, 2022年 11 月 07日 下午 10:29:54
主题: [blog article] Howto migrate a real-life batch pipeline from the DataSet
API to the DataStream API
Hi everyone,
In case some of you are interested, I just posted a blog article about
migrating a real-life batch pipeline from the DataSet API to the
DataStream API:
https://echauchot.blogspot.com/2022/11/flink-howto-migrate-real-life-batch.html
<https://echauchot.blogspot.com/2022/11/flink-howto-migrate-real-life-batch.html
>
Best
Etienne
