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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-4069) Use read concern majority when connected to a replica set
Date Thu, 08 Dec 2016 12:38:59 GMT

    [ https://issues.apache.org/jira/browse/OAK-4069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15732092#comment-15732092

Marcel Reutegger commented on OAK-4069:

The command serverStatus requires a user to have the clusterMonitor role. Can you add warning
when the connection is authenticated and the user does not have that role assigned? I understand
in that case the MongoDocumentStore would stay with the default read concern even if the majority
read concern option is enabled on the server.

It would also be good to run some performance tests to see whether this new default has an
impact in a replica set.

> Use read concern majority when connected to a replica set
> ---------------------------------------------------------
>                 Key: OAK-4069
>                 URL: https://issues.apache.org/jira/browse/OAK-4069
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: mongomk
>            Reporter: Tomek Rękawek
>            Assignee: Tomek Rękawek
>              Labels: resilience
>             Fix For: 1.6, 1.5.16
>         Attachments: OAK-4069.patch
> Mongo 3.2 introduces new query option: {{readConcern}}. It allows to read only these
changes that have been already committed to the majority of secondary instances.
> It prevents stale reads - a situation in which a change has been committed on the primary
(and read from it), but due to the network partition a new primary is elected and the change
is rolled back.
> We should use this new option (together with {{w:majority}} implemented in OAK-3554)
when running Oak on MongoDB replica set.
> References:
> * [Jepsen: MongoDB stale reads|https://aphyr.com/posts/322-jepsen-mongodb-stale-reads]
> * [MongoDB documentation: Read Concern in|https://docs.mongodb.org/manual/reference/read-concern/]

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