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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 Wed, 14 Dec 2016 07:32:58 GMT

    [ https://issues.apache.org/jira/browse/OAK-4069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15747557#comment-15747557

Marcel Reutegger commented on OAK-4069:

Patch looks good. I noticed just one minor issue with {{DocumentMK.Builder.setMongoDB(DB,
MongoStatus, int)}}. It does not set {{mongoStatus}} in the builder and {{MongoDocumentStore}}
therefore needs to calculate a new status in the constructor.

> 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-4069-2.patch, OAK-4069-3.patch, 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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