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Re: [DISCUSS] Integrate Flink SQL well with Hive ecosystem

Hi Jörn,

Thanks for your feedback. Yes, I think Hive on Flink makes sense and in fact it is one of the two approaches that I named in the beginning of the thread. As also pointed out there, this isn't mutually exclusive from work we proposed inside Flink and they target at different user groups and user cases. Further, what we proposed to do in Flink should be a good showcase that demonstrate Flink's capabilities in batch processing and convince Hive community of the worth of a new engine. As you might know, the idea encountered some doubt and resistance. Nevertheless, we do have a solid plan for Hive on Flink, which we will execute once Flink SQL is in a good shape.

I also agree with you that Flink SQL shouldn't be closely coupled with Hive. While we mentioned Hive in many of the proposed items, most of them are coupled only in concepts and functionality rather than code or libraries. We are taking the advantage of the connector framework in Flink. The only thing that might be exceptional is to support Hive built-in UDFs, which we may not make it work out of the box to avoid the coupling. We could, for example, require users bring in Hive library and register themselves. This is subject to further discussion.

#11 is about Flink runtime enhancement that is meant to make task failures more tolerable (so that the job don't have to start from the beginning in case of task failures) and to make task scheduling more resource-efficient. Flink's current design in those two aspects leans more to stream processing, which may not be good enough for batch processing. We will provide more detailed design when we get to them.

Please let me know if you have further thoughts or feedback.


Sender:Jörn Franke <jornfranke@xxxxxxxxx>
Sent at:2018 Oct 11 (Thu) 13:54
Recipient:Xuefu <xuefu.z@xxxxxxxxxxxxxxx>
Cc:vino yang <yanghua1127@xxxxxxxxx>; Fabian Hueske <fhueske@xxxxxxxxx>; dev <dev@xxxxxxxxxxxxxxxx>; user <user@xxxxxxxxxxxxxxxx>
Subject:Re: [DISCUSS] Integrate Flink SQL well with Hive ecosystem

Would it maybe make sense to provide Flink as an engine on Hive („flink-on-Hive“)? Eg to address 4,5,6,8,9,10. this could be more loosely coupled than integrating hive in all possible flink core modules and thus introducing a very tight dependency to Hive in the core.
1,2,3 could be achieved via a connector based on the Flink Table API.
Just as a proposal to start this Endeavour as independent projects (hive engine, connector) to avoid too tight coupling with Flink. Maybe in a more distant future if the Hive integration is heavily demanded one could then integrate it more tightly if needed. 

What is meant by 11?
Am 11.10.2018 um 05:01 schrieb Zhang, Xuefu <xuefu.z@xxxxxxxxxxxxxxx>:

Hi Fabian/Vno,

Thank you very much for your encouragement inquiry. Sorry that I didn't see Fabian's email until I read Vino's response just now. (Somehow Fabian's went to the spam folder.)

My proposal contains long-term and short-terms goals. Nevertheless, the effort will focus on the following areas, including Fabian's list:

1. Hive metastore connectivity - This covers both read/write access, which means Flink can make full use of Hive's metastore as its catalog (at least for the batch but can extend for streaming as well).
2. Metadata compatibility - Objects (databases, tables, partitions, etc) created by Hive can be understood by Flink and the reverse direction is true also.
3. Data compatibility - Similar to #2, data produced by Hive can be consumed by Flink and vise versa.
4. Support Hive UDFs - For all Hive's native udfs, Flink either provides its own implementation or make Hive's implementation work in Flink. Further, for user created UDFs in Hive, Flink SQL should provide a mechanism allowing user to import them into Flink without any code change required.
5. Data types -  Flink SQL should support all data types that are available in Hive.
6. SQL Language - Flink SQL should support SQL standard (such as SQL2003) with extension to support Hive's syntax and language features, around DDL, DML, and SELECT queries.
7.  SQL CLI - this is currently developing in Flink but more effort is needed.
8. Server - provide a server that's compatible with Hive's HiverServer2 in thrift APIs, such that HiveServer2 users can reuse their existing client (such as beeline) but connect to Flink's thrift server instead.
9. JDBC/ODBC drivers - Flink may provide its own JDBC/ODBC drivers for other application to use to connect to its thrift server
10. Support other user's customizations in Hive, such as Hive Serdes, storage handlers, etc.
11. Better task failure tolerance and task scheduling at Flink runtime.

As you can see, achieving all those requires significant effort and across all layers in Flink. However, a short-term goal could  include only core areas (such as 1, 2, 4, 5, 6, 7) or start  at a smaller scope (such as #3, #6).

Please share your further thoughts. If we generally agree that this is the right direction, I could come up with a formal proposal quickly and then we can follow up with broader discussions.


Sender:vino yang <yanghua1127@xxxxxxxxx>
Sent at:2018 Oct 11 (Thu) 09:45
Recipient:Fabian Hueske <fhueske@xxxxxxxxx>
Subject:Re: [DISCUSS] Integrate Flink SQL well with Hive ecosystem

Hi Xuefu,

Appreciate this proposal, and like Fabian, it would look better if you can give more details of the plan.

Thanks, vino.

Fabian Hueske <fhueske@xxxxxxxxx> 于2018年10月10日周三 下午5:27写道:
Hi Xuefu,

Welcome to the Flink community and thanks for starting this discussion! Better Hive integration would be really great!
Can you go into details of what you are proposing? I can think of a couple ways to improve Flink in that regard:

* Support for Hive UDFs
* Support for Hive metadata catalog
* Support for HiveQL syntax
* ???

Best, Fabian

Am Di., 9. Okt. 2018 um 19:22 Uhr schrieb Zhang, Xuefu <xuefu.z@xxxxxxxxxxxxxxx>:
Hi all,

Along with the community's effort, inside Alibaba we have explored Flink's potential as an execution engine not just for stream processing but also for batch processing. We are encouraged by our findings and have initiated our effort to make Flink's SQL capabilities full-fledged. When comparing what's available in Flink to the offerings from competitive data processing engines, we identified a major gap in Flink: a well integration with Hive ecosystem. This is crucial to the success of Flink SQL and batch due to the well-established data ecosystem around Hive. Therefore, we have done some initial work along this direction but there are still a lot of effort needed.

We have two strategies in mind. The first one is to make Flink SQL full-fledged and well-integrated with Hive ecosystem. This is a similar approach to what Spark SQL adopted. The second strategy is to make Hive itself work with Flink, similar to the proposal in [1]. Each approach bears its pros and cons, but they don’t need to be mutually exclusive with each targeting at different users and use cases. We believe that both will promote a much greater adoption of Flink beyond stream processing.

We have been focused on the first approach and would like to showcase Flink's batch and SQL capabilities with Flink SQL. However, we have also planned to start strategy #2 as the follow-up effort.

I'm completely new to Flink(, with a short bio [2] below), though many of my colleagues here at Alibaba are long-time contributors. Nevertheless, I'd like to share our thoughts and invite your early feedback. At the same time, I am working on a detailed proposal on Flink SQL's integration with Hive ecosystem, which will be also shared when ready.

While the ideas are simple, each approach will demand significant effort, more than what we can afford. Thus, the input and contributions from the communities are greatly welcome and appreciated.




[1] https://issues.apache.org/jira/browse/HIVE-10712
[2] Xuefu Zhang is a long-time open source veteran, worked or working on many projects under Apache Foundation, of which he is also an honored member. About 10 years ago he worked in the Hadoop team at Yahoo where the projects just got started. Later he worked at Cloudera, initiating and leading the development of Hive on Spark project in the communities and across many organizations. Prior to joining Alibaba, he worked at Uber where he promoted Hive on Spark to all Uber's SQL on Hadoop workload and significantly improved Uber's cluster efficiency.