[DOCS-4045] Clarify that write concern majority includes all members Created: 16/Sep/14  Updated: 18/Nov/14  Resolved: 17/Nov/14

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: v1.3.12, v1.3.14

Type: Bug Priority: Critical - P2
Reporter: Jeremy Mikola Assignee: Sam Kleinman (Inactive)
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
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Participants:
Days since reply: 9 years, 13 weeks, 1 day ago

 Description   

In PHP-1222, a user expected that the "majority" write concern would only consider data-bearing nodes. scotthernandez provided me with a helpful explanation for why it needs to count all nodes, as the goal is to avoid data loss due to roll-back. It would be helpful if we explained this with a blurb in the documentation.

http://docs.mongodb.org/manual/core/write-concern/ talks about "majority" persisting data to storage nodes, but it doesn't address arbiters at all. Obviously, they don't hold data, but they are counted in determining the "majority".

He also clarified that "majority" means something else when referring to election voting (it depends more on voters and vote weights than physical nodes), but I don't think we need to clarify that with this ticket.



 Comments   
Comment by Githook User [ 18/Nov/14 ]

Author:

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

Message: DOCS-4045: edits to read-uncommited
Branch: master
https://github.com/mongodb/docs/commit/5296b324e4fb7b6bd3fce80012d1ef8216f130ac

Comment by Kevin Pulo [ 12/Nov/14 ]

This change is not correct. w:majority does NOT refer to a majority of the voting members. w:majority means a majority of ALL replica set members. The code is very straightforward on this, it is basically just "number of members / 2 + 1" (except if there are more arbiters than non-arbiters). Please update the language to make it clear that when computing w:majority, all members are counted, including arbiters, non-voting members, slave delayed members, and hidden members.

Note that this behaviour is changing in 2.8 to be a majority of voting members, see SERVER-14403, which is the better behaviour on many levels. But the docs for 2.6 and earlier must still be fixed.

Comment by Githook User [ 03/Oct/14 ]

Author:

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

Message: DOCS-4045: write concern includes arbiters and is based on votes
Branch: master
https://github.com/mongodb/docs/commit/eef5ff45eb1c58646f995439714fc9f6dd9d874a

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