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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-3554) Use write concern of w:majority when connected to a replica set
Date Wed, 11 Nov 2015 15:43:11 GMT

    [ https://issues.apache.org/jira/browse/OAK-3554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15000543#comment-15000543
] 

Marcel Reutegger commented on OAK-3554:
---------------------------------------

For now I didn't change the write concern when connected to a single MongoDB instance. The
performance impact with the default journalCommitInterval is too big for a setup that is not
recommended in production. I think we should create a separate issue for this case and discuss
options.

When connected to a replica set, MongoMK now uses the MAJORITY write concern, unless the the
MongoDB URI has an explicit write concern set. The DocumentMK.Builder now checks if the write
concern is sufficient for the setup and logs a warning.

I didn't change the behavior of the existing setMongoDB() methods on the builder. The expectation
now is that a client knows what it is doing when it passes a DB object to the builder and
MongoMK will use the current set write concern on the DB. Though, it does perform a check
and logs the above mentioned warning if the write concern is considered insufficient.

Done in trunk: http://svn.apache.org/r1713875 and http://svn.apache.org/r1713876

> Use write concern of w:majority when connected to a replica set
> ---------------------------------------------------------------
>
>                 Key: OAK-3554
>                 URL: https://issues.apache.org/jira/browse/OAK-3554
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: core, mongomk
>            Reporter: Chetan Mehrotra
>            Assignee: Marcel Reutegger
>              Labels: resilience
>             Fix For: 1.4
>
>
> Currently while connecting to Mongo MongoDocumentStore relies on default write concern
provided as part of mongouri. 
> Recently some issues were seen where Mongo based Oak was connecting to 3 member replica
set and there were frequent replica state changes due to use of VM for Mongo. This caused
data loss and corruption of data in Oak.
> To avoid such situation Oak should default to write concern of majority by default. If
some write concern is specified as part of mongouri then that should take precedence. This
would allow system admin to take the call of tweaking write concern if required and at same
time allows Oak to use the safe write concern.



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