[jira] [Created] (FLINK-20614) Registered sql drivers not deregistered after task finished in session cluster

["Kezhu Wang (Jira)" <ji...@apache.org>]

Kezhu Wang created FLINK-20614:
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             Summary: Registered sql drivers not deregistered after task finished in session cluster
                 Key: FLINK-20614
                 URL: https://issues.apache.org/jira/browse/FLINK-20614
             Project: Flink
          Issue Type: Bug
          Components: Connectors / JDBC, Runtime / Task
    Affects Versions: 1.12.0, 1.13.0
            Reporter: Kezhu Wang


{{DriverManager}} keeps registered drivers in its internal data structures which prevents they from gc after task finished. I confirm it in standalone session cluster by observing that {{ChildFirstClassLoader}} could not be reclaimed after several {{GC.run}}, it should exist in all session clusters.

Tomcat documents [this|https://ci.apache.org/projects/tomcat/tomcat85/docs/jndi-datasource-examples-howto.html#DriverManager,_the_service_provider_mechanism_and_memory_leaks] and fixes/circumvents this with [JdbcLeakPrevention|https://github.com/apache/tomcat/blob/master/java/org/apache/catalina/loader/JdbcLeakPrevention.java#L30].

Should we solve this in runtime ? Or treat it as connector and clients' responsibility to solve it using {{RuntimeContext.registerUserCodeClassLoaderReleaseHookIfAbsent}} or similar ?

Personally, it would be nice to solve in runtime as a catch-all to avoid memory-leaking and provide consistent behavior to clients cross per-job and session mode.



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