Re: Distribute DataSet to subset of nodes

Posted by Stefan Bunk on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Distribute-DataSet-to-subset-of-nodes-tp2814p2842.html

Hi Fabian,

I think we might have a misunderstanding here. I have already copied the first file to five nodes, and the second file to five other nodes, outside of Flink. In the open() method of the operator, I just read that file via normal Java means. I do not see, why this is tricky or how HDFS should help here.

Then, I have a normal Flink DataSet, which I want to run through the operator (using the previously read data in the flatMap implementation). As I run the program several times, I do not want to broadcast the data every time, but rather just copy it on the nodes, and be fine with it.

Can you answer my question from above? If the setParallelism-method works and selects five nodes for the first flatMap and five _other_ nodes for the second flatMap, then that would be fine for me if there is no other easy solution.

Thanks for your help!

Best

Stefan

On 14 September 2015 at 22:28, Fabian Hueske <[hidden email]> wrote:

Hi Stefan,

forcing the scheduling of tasks to certain nodes and reading files from the local file system in a multi-node setup is actually quite tricky and requires a bit understanding of the internals.

It is possible and I can help you with that, but would recommend to use a shared filesystem such as HDFS if that is possible.

Best, Fabian

2015-09-14 19:16 GMT+02:00 Stefan Bunk <[hidden email]>:

Hi,

actually, I am distributing my data before the program starts, without using broadcast sets.

However, the approach should still work, under one condition:

DataSet mapped1 = data.flatMap(yourMap).withBroadcastSet(smallData1,"data").setParallelism(5);
DataSet mapped2 = data.flatMap(yourMap).withBroadcastSet(smallData2,"data").setParallelism(5);

Is it guaranteed, that this selects a disjoint set of nodes, i.e. five nodes for mapped1 and five other nodes for mapped2?

Is there any way of selecting the five nodes concretely? Currently, I have stored the first half of the data on nodes 1-5 and the second half on nodes 6-10. With this approach, I guess, nodes are selected randomly so I would have to copy both halves to all of the nodes.

Best,

Stefan