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

["Tugdual Grall (JIRA)" <ji...@apache.org>]

Tugdual Grall created DRILL-4882:
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             Summary: 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: 1.8.0, 1.7.0, 1.6.0
         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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