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 <[email protected]>
To: [email protected]
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 <[email protected]>
wrote:
Oh that's good to know. I assume it works like this:
https://en.wikipedia.org/wiki/ Hash_function#Hashing_ uniformly_distributed_data
On Wed, Aug 10, 2016 at 6:23 PM, Nathan Leung <[email protected]> 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" <[email protected] om> wrote:
Hi,
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?
--
Regards,Navin
--
Regards,Navin
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Regards,Navin
