What is the best way to manage the inputs from more than one bolt?

[fedelemantuano]

Is there a standard method to manage the inputs from more than one bolt?

I have three bolts (A, B, C) that do something. Then there is bolt MERGE that should merge A, B and C emits and output merge result.

I'm using a RAM storage in MERGE bolt, and I waiting tuple from A, B, C. But is this the best way?

[dan-blanchard]

In the past I've done pretty much what you have when dealing with this issue:

1. Use a fields grouping on the ID that we will use for joining.
2. Store the values we've received for a given ID until we have all of the ones we were expecting.
3. Process the values we stored when we have them all for a given ID.

One tip I can offer is that rather than hard-coding the list of inputs your bolt is expecting, you can actually just set that list to list(self.context['source->stream->grouping'].keys()) if you're using a version of Storm newer than 0.10.0. That will contain a list of all of the bolts that feed into the current one. You can see more details about what kind of info you can pull out of Bolt.context here.