[jira] [Created] (FLINK-3315) Fix Slot Sharing in Streaming API

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

Aljoscha Krettek created FLINK-3315:
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             Summary: Fix Slot Sharing in Streaming API
                 Key: FLINK-3315
                 URL: https://issues.apache.org/jira/browse/FLINK-3315
             Project: Flink
          Issue Type: Improvement
          Components: Streaming
    Affects Versions: 1.0.0
            Reporter: Aljoscha Krettek
            Assignee: Aljoscha Krettek


Right now, the slot sharing/resource group logic is a bit "nebulous". The slot sharing group that operators are put in depends on the order in which operations are created. For example, in this case:

{code}
Source a = env.source()
Source b = env.source()

a.map().startNewResourceGroup().sink() 
b.map().sink()
{code}

We end up with two resource groups:
- group 1: source a
- group 2: map(), sink(), source b, map(), sink()

The reason is that the slot sharing id is incremented when transforming the {{startNewResouceGroup()}} call and all operators that are transformed afterwards in graph traversal get that new slot sharing id.

(There is also {{isolateResources()}} which can be used to isolate an operator.)

What I propose is to remove {{startNewResourceGroup()}} and {{isolateResouces()}} and replace it with {{slotSharingGroup(String)}}. By default, operations would be in slot sharing group "default". This allows very fine grained control over what operators end up in which slot sharing group. For example, I could have this topology:

{code}
Source a = env.source().slotSharingGroup("sources")
Source b = env.source().slotSharingGroup("sources")

a.map().slotSharingGroup("heavy a").sink().slotSharingGroup("sinks") 
b.map().slotSharingGroup("heavy b").sink().slotSharingGroup("sinks")
{code}

Which would isolate the lightweight sources and sinks in a group and put heavy operations inside their own slot groups.

This is a bit more low level than the previous API and requires more calls than a simple {{startNewResourceGroup()}} but I think not many people would use this feature and this design makes it very clear what operations end up in the same group.



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