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From Gireesh Ramji <>
Subject Re: How long until fields grouping gets overwhelmed with data?
Date Thu, 11 Aug 2016 09:06:34 GMT
It does not matter who hashes it as long as they all use the same hash function it will go
to the same bolt

      From: Navin Ipe <>
 Sent: Thursday, August 11, 2016 4:56 PM
 Subject: Re: How long until fields grouping gets overwhelmed with data?
If the hash is dynamically computed and is stateless, then that brings up one more question.

Let's say there are two spout classes S1 and S2. I create 10 tasks of S1 and 10 tasks of S2.
There are 10 tasks of a bolt B.

S1 and S2 are fieldsGrouped with B.

I receive data x in S1 and another data x in S2. 

If S1's emit of x goes to task1 of B, then will S2's emit of x also go to task1 of B?

Basically the question is: Is the hash value decided by the Spout or by Storm? Because if
it is decided by the spout, then S1's emit of x can go to task 1 but S2's emit of x might
go to some other task of the bolt, and that won't serve the purpose of someone who wants all
x'es to go to one bolt.

On Wed, Aug 10, 2016 at 8:58 PM, Navin Ipe <> wrote:

Oh that's good to know. I assume it works like this: Hash_function#Hashing_

On Wed, Aug 10, 2016 at 6:23 PM, Nathan Leung <> wrote:

It's based on a modulo of a hash of the field. The fields grouping is stateless.
On Aug 10, 2016 8:18 AM, "Navin Ipe" <navin.ipe@searchlighthealth.c om> wrote:


For spouts to be able to continuously send a fields grouped tuple to the same bolt, it would
have to store a key value map something like this, right?

field1023 ---> Bolt1
field1343 ---> Bolt3
field1629 ---> Bolt5
field1726 ---> Bolt1
field1481 ---> Bolt3

So if my topology runs for a very long time and the spout generates many unique field values,
won't this key value map run out of memory eventually? 

OR is there a failsafe or a map limit that Storm has to handle this without crashing?

If memory problems could happen, what would be an alternative way to solve this problem where
many unique fields could get generated over time?




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