See
https://github.com/apache/storm/blob/21bb1388414d373572779289edc785c7e5aa52aa/storm-client/src/jvm/org/apache/storm/daemon/GrouperFactory.java#L174
and
https://github.com/apache/storm/blob/21bb1388414d373572779289edc785c7e5aa52aa/storm-client/src/jvm/org/apache/storm/utils/TupleUtils.java#L38
.
The "key" field value will be hashed using Arrays.deepHashCode, so if you
have two tuples t1 and t2, and hashCode(t1["key"]) == hashCode(t2["key"]),
then t1 and t2 will go to the same task in "gamma".
Den fre. 23. nov. 2018 kl. 09.06 skrev <bogun.dmit...@gmail.com>:
> Hi.
>
> I have a question, regarding fields grouping. In documentation we have:
> ```
> Fields grouping: The stream is partitioned by the fields specified in the
> grouping. For example, if the stream is grouped by the "user-id" field,
> tuples with the same "user-id" will always go to the same task, but tuples
> with different "user-id"'s may go to different tasks.
> ```
> It is clear, when we have single point-to-point connection i.e [A]
> --sream--> [B]. But if we have some bolt that consume 2 stream from 2
> different bolts but use same key(also streams have same "format") for
> fields grouping. Something like this:
>
> ```
> TopologyBuilder topology = new TopologyBuilder();
>
> // ----
>
> topology.setBolt("alpha", new AlphaBolt(), alphaScaleFactor);
>
> topology.setBolt("beta", new BetaBolt(), betaScaleFactor);
>
> Fields grouping = new Fields("key");
> topology.setBolt("gamma", new GammaBolt(), gammaScaleFactor)
> .fieldsGrouping("alpha", "alpha-stream", grouping)
> .fieldsGrouping("beta", "beta-stream", grouping);
>
> // ----
> ```
>
> Is there any guarantee that both streams will be partitioned in same way
> and tuples with same value in "key" field in both streams will be directed
> into same instance/task of "gamma" bolt?
>
