[DOCS-5701] Jumbo chunks are never cleared automatically Created: 23/Jun/15  Updated: 30/Oct/23  Resolved: 01/Nov/22

Status: Closed
Project: Documentation
Component/s: manual, Server
Affects Version/s: None
Fix Version/s: Server_Docs_20231030

Type: Bug Priority: Major - P3
Reporter: Kevin Pulo Assignee: Unassigned
Resolution: Won't Fix Votes: 2
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to SERVER-13024 Clear the 'jumbo' flag from the chunk... Blocked
related to DOCS-4163 Document how to manually reset Jumbo ... Closed
Participants:
Days since reply: 1 year, 14 weeks, 1 day ago
Epic Link: DOCSP-1769

 Description   

This page:

http://docs.mongodb.org/manual/tutorial/clear-jumbo-flag/

erroneously claims

If the chunk size no longer hits the limits, MongoDB clears the jumbo flag for the chunk when the mongos reloads or rewrites the chunk metadata.

This is not true.

It looks like DOCS-4163 missed that SERVER-13024 (which it references) is not actually resolved?

This ticket is to request that the above sentence be replaced by one that explains when jumbo is cleared (currently only on successful chunk split), and that this means sometimes it needs to be cleared manually.



 Comments   
Comment by Education Bot [ 01/Nov/22 ]

Hello! This ticket has been closed due to inactivity. If you believe this ticket is still important, please reopen it and leave a comment to explain why. Thank you!

Comment by Kevin Pulo [ 26/Jun/15 ]

Oops, sorry about this — my testing wasn't sufficient. The jumbo flag can be cleared in certain circumstances, which (at the moment) are independent of whether or not the chunk is still jumbo. However, if the flag gets cleared, and the chunk is still actually jumbo, then at some later time it'll get marked jumbo again.

The circumstances when jumbo will or won't be cleared are pretty complicated, but I think that "when the mongos reloads or rewrites the chunk metadata" isn't terribly useful for most users.

Based on this, my suggestion is to change the second paragraph to something like:

MongoDB clears the jumbo flag in certain circumstances, such as when the chunk is split or migrated. However, if the chunk still satisfies the above criteria it may be marked as jumbo again.

I think it's also worth mentioning on this page the implications of jumbo chunks, namely, that the balancer does not attempt to split or migrate them.

EDIT: I also think it might be useful to specify in the first paragraph that one of the leading causes of large chunks that cannot be split is poor shard key cardinality (with a link to the Considerations for Selecting Shard Key).

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