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