Re: DB connection and query inside map function

Posted by Fabian Hueske-2 on Nov 28, 2016; 8:50am
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/DB-connection-and-query-inside-map-function-tp10342p10344.html

Hi Anastasios,

that's certainly possible. The most straight-forward approach would be a synchronous call to the database.

Because only one request is active at the same time, you do not need a thread pool.

You can establish the connection in the open() method of a RichMapFunction. The problem with this approach is that the synchronous requests can significantly increase the latency.

Doing the calls asynchronously and using a thread pool is not very easy because this would need to be integrated with Flink's checkpointing mechanism.

In fact, there is an effort to add a special Map operator that supports asynchronous calls (see FLIP-12 [1]).

We expect this to be included in the next minor release, Flink 1.2.

Hope this helps,

Fabian

[1] https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=65870673

2016-11-27 22:11 GMT+01:00 Anastasios Skarlatidis <[hidden email]>:

Hi! 

I am new to Apache Flink and I would like to ask what is the best way to query a relational DB inside a map function, in order to enrich the streaming data. Consider, for example, that I have a KeyedStream[Int, String] and I would like to query the database based on the Int value inside a map function `stream.map(v: Int => <<some SQL query>> )`. 

Is it possible to have a connection pooler per worker nod,e in order to be used inside each map function call?

Best,

Anastasios