Sorabh Hamirwasia created DRILL-6063:
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Summary: Set correct ThreadContext ClassLoader before using Hadoop
Configuration class in DrillClient
Key: DRILL-6063
URL: https://issues.apache.org/jira/browse/DRILL-6063
Project: Apache Drill
Issue Type: Improvement
Components: Client - Java
Affects Versions: 1.11.0
Reporter: Sorabh Hamirwasia
Assignee: Sorabh Hamirwasia
Drill Client uses Hadoop Configuration class in security mechanism factories.
Configuration class internally uses ThreadContext class loader to get the
default resources for configurations. When Drill JDBC driver is used with 3rd
party tool like Squirrel then it creates a class loader with all Drill Driver
related dependencies. This class loader is used to instantiate an object of
Driver class in a separate thread. But the thread context class loader has
dependencies related to Squirrel only. As a result of this when Hadoop
Configuration class tries to load the resources with default values it doesn't
find them in class path.
If we specify hadoop dependencies in Squirrel's classpath instead of Driver
dependencies class path then it will work since Thread Context class loader
will have Hadoop libraries loaded too and will find the resources. But this is
not good as it is tying up one Squirrel instance with one version of Hadoop
which might not be true in all the cases like here when same Squirrel instance
can be used to load multiple versions of Drill Driver having different hadoop
version dependencies.
To deal with this issue a simple fix is to set the Thread Context class loader
to be same as Drill Driver dependencies class loader before accessing Hadoop
Configuration class in Drill Client and later restore it back.
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