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https://issues.apache.org/jira/browse/SAMZA-1202?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jagadish reassigned SAMZA-1202:
-------------------------------
Assignee: Jagadish
> Multiple calls to `graph.getInputStream()` with the same streamId results in
> non-deterministic behavior
> -------------------------------------------------------------------------------------------------------
>
> Key: SAMZA-1202
> URL: https://issues.apache.org/jira/browse/SAMZA-1202
> Project: Samza
> Issue Type: Bug
> Reporter: Jagadish
> Assignee: Jagadish
>
> Consider the following code-snippet that invokes graph.getInputStream
> multiple times with the same streamId (but with different Message Builders).
> {code}
> BiFunction<String, String, String> msgBuilder1 = (k, v) -> v;
> BiFunction<String, String, Integer> msgBuilder2 = (k, v) -> new
> Integer(v);
> graph.getInputStream("page-views", msgBuilder2);
> MessageStream<String> pageViews1 = graph.getInputStream("page-views",
> msgBuilder1);
> pageViews1.map(..)
> .filter(..)
> .window(..)
> .sink(..)
> {code}
> TL;DR:
> The above snippet could result in messages not being propagated to the
> operator chain depending on the iteration order of Java Hashmaps.
> *Here is the exact sequence:*
> 1. User creates two `MessageStream`s by multiple calls to
> `graph.getInputStream()` with the same streamId but different MessageBuilders.
> 2. This invokes StreamGraphImpl#getInputStream, which obtains a StreamSpec
> instance for the streamId and adds it to its map.
> 3. During the wire-up of the physical DAG in `StreamOperatorTask`,
> streamGraph.getInputStreams().forEach((streamSpec, inputStream)` is invoked.
> 4. Depending on the iteration order in which
> `streamGraph.getInputStreams().forEach((streamSpec, inputStream)` returns its
> results, we could end up with a different representation of the DAG (with the
> latest streamSpec clobbering it's previous one).
> There are 2 approaches to solve this:
> *Approach 1:*
> Add additional validation to prevent this scenario from happening. We will
> validate multiple calls made to `graph.getInputStream` with the same
> streamId, and throw an IllegalArgumentException.
> *Approach 2:*
> Maintain a `MultiMap` instead of a `HashMap` so that the latest `StreamSpec`
> does not clobber the earlier one.
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