[DOCS-4204] Comment on: "manual/tutorial/choose-a-shard-key.txt" Created: 17/Oct/14  Updated: 14/Dec/16  Resolved: 17/Oct/14

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: v1.3.12

Type: Bug Priority: Major - P3
Reporter: Ruby Boyarski Assignee: Sam Kleinman (Inactive)
Resolution: Done Votes: 0
Labels: collector-298ba4e7
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified
Environment:

Location: http://docs.mongodb.org/manual/tutorial/choose-a-shard-key/#sharding-shard-key-cardinality
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124 Safari/537.36
Referrer: http://docs.mongodb.org/manual/tutorial/choose-a-shard-key/
Screen Resolution: 1440 x 900
repo: docs
source: tutorial/choose-a-shard-key


Participants:
Days since reply: 9 years, 17 weeks, 5 days ago

 Description   

Thanks for the great documentation.
We believe it's missing a very important fact about large chunks, which could be cause by incorrect selection of a shard key. Unsplittable large chunks will not be moved by the balancer. Thus, making them static to the shard they've been created on and never be able to move them, in case there's a need for it.
In "Scaling MongoDB" Kristina Chodorow writes "If a chunk gets too big, MongoDB will refuse to move it". This comment is spot on and should be in the official documentation as it affects the shard key decision.



 Comments   
Comment by Githook User [ 17/Oct/14 ]

Author:

{u'username': u'tychoish', u'name': u'Sam Kleinman', u'email': u'samk@10gen.com'}

Message: DOCS-4204: adding a note about cardinality and large chunks
Branch: master
https://github.com/mongodb/docs/commit/63c61a8639485f87b5f4c30fc3a16108b985cecb

Comment by Gianfranco Palumbo [ 17/Oct/14 ]

Hi Ruby,

Thanks for reporting this.
You're right this fact is not mentioned in this page.

While we do have it here it's true that if you choose a shard key that does not have high cardinality some chunks could get too big to be moved.

Regards,
Gianfranco

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