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https://issues.apache.org/jira/browse/DRILL-3822?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14903675#comment-14903675
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Jacques Nadeau commented on DRILL-3822:
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The changes in the shading behavior were to avoid the situation where
pathScanner is going beyond its context to find information. It used to
traverse the entire classloader hierarchy. That doesn't make sense when you're
in an app server scenario. Instead we should be constrained in our behavior.
The question is why this fix [1] is causing issues in this situation.
[1]
https://github.com/apache/drill/commit/4e3b7dc0333a01e72d0ea9256331ea1e1dd51181?diff=split#diff-13e50b60c90f8ea8fe55481963573776R145
> PathScanner fails to find jdbc-all's drill-module.conf in SQuirreL
> ------------------------------------------------------------------
>
> Key: DRILL-3822
> URL: https://issues.apache.org/jira/browse/DRILL-3822
> Project: Apache Drill
> Issue Type: Bug
> Components: Client - JDBC
> Affects Versions: 1.2.0
> Reporter: Krystal
> Assignee: Daniel Barclay (Drill)
> Attachments: squirrel.log
>
>
> git.commit.id.abbrev=3c89b30
> I used the latest drill-jdbc-all-1.2.0-SNAPSHOT.jar against the SQuirreL SQL
> application. I got the following error when trying to connect to the drill
> data source:
> {noformat}
> ERROR net.sourceforge.squirrel_sql.client.gui.db.ConnectToAliasCallBack -
> Unexpected Error occurred attempting to open an SQL connection.
> java.util.concurrent.ExecutionException: java.lang.RuntimeException:
> oadd.com.typesafe.config.ConfigException$Missing: No configuration setting
> found for key 'drill.exec'
> Full error message is in the attached file.
> {noformat}
> We turned on logging and found that the jdbc-all Jar file's
> {{drill-module.conf}} file was not being found (explaining why the
> configuration key {{drill.exec}} wasn't found).
> After further investigation, it seems that {{PathScanner}} directly uses the
> system class loader, bypassing the context class loader.
> (After drill-jdbc-all-1.2.0-SNAPSHOT.jar was changed from being listed in
> SQuirreL's "additional class paths" (presumably being loaded by a special
> class loader) to being copied into SQuirreL's Jar file directory (and
> therefore loaded by the system class loader), SQuirreL worked. (Apparently,
> {{PathScanner}} was then able to find {{drill-module.conf}} in the JDBC-all
> Jar file and load it, so the later reference to {{drill.exec}} no longer
> failed.)
> Also, SQuirreL works correctly with drill-1.1's JDBC-all Jar file, and there
> were some recent changes to {{PathScanner}} related to class loaders.)
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