[jira] [Commented] (DRILL-4882) Drill does not work when it has only access to "secondary nodes"

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15565746#comment-15565746 ] 

ASF GitHub Bot commented on DRILL-4882:
---------------------------------------

GitHub user tgrall opened a pull request:

    https://github.com/apache/drill/pull/609

    DRILL-4882 - Support for MongoDB Direct Connection to a node in a Replica Set.

    See issue DRILL-4882
    
    In some case, for analytics the applicatio, Drill, has to connect to node directly without access the replica set or shard globally.
    
    The new configuration option `direct-connection` true|false allows drillbit to be directly connected to a node.
    
    References:
    * [Connection String](http://mongodb.github.io/mongo-java-driver/3.0/driver/reference/connecting/connection-settings/)
    * [Direct Connection term](https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst#terms)


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/tgrall/drill DRILL-4882

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/drill/pull/609.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #609
    
----

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> Drill does not work when it has only access to "secondary nodes"
> ----------------------------------------------------------------
>
>                 Key: DRILL-4882
>                 URL: https://issues.apache.org/jira/browse/DRILL-4882
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - MongoDB
>    Affects Versions: 1.6.0, 1.7.0, 1.8.0
>         Environment: Drill Stand Alone
> Drill in MapR
>            Reporter: Tugdual Grall
>            Priority: Minor
>
> In some deployments, especially when doing analytics on MongoDB, the application, Drill in this case, only have access to secondary nodes. 
> This is a common choice to avoid overloading the Mongo cluster.
> When we have such configuration Drill fail with various exception related to timeout/primary read preference.
> This is due to the fact that some of the "Schema Oriented" methods of MongoDriver are forcing the read preference to primary. The methods are used in the following place in Drill:
> 1-
> https://github.com/apache/drill/blob/1.8.0/contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/schema/MongoSchemaFactory.java#L89
> 2-
> https://github.com/apache/drill/blob/1.8.0/contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/schema/MongoSchemaFactory.java#L109
> and also the Run command to get information about the type of topology (sharded or not):
> 3- 
> https://github.com/apache/drill/blob/1.8.0/contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/MongoGroupScan.java#L167
> 3- could be fixed by simply adding a ReadPreference.primaryPreferred() but not sufficient since we need to have 1 & 2 fixed



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