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From Tomek Rękawek (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-4069) Use read concern majority when connected to a replica set
Date Thu, 08 Dec 2016 11:41:00 GMT

    [ https://issues.apache.org/jira/browse/OAK-4069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15731938#comment-15731938

Tomek Rękawek commented on OAK-4069:

Got it. I've uploaded new patch, it'll only enable the read concern = majority if:

* no read concern level is passed in the URI (see {{DocumentMK.Builder#setMongoDB()}}) and
* the server supports it (see {{MongoStatus#supportsReadConcern}}).

> 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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