mbutrovich commented on issue #4611:
URL: 
https://github.com/apache/datafusion-comet/issues/4611#issuecomment-4672188345

   Thanks for the detailed report and the reproducer repo, @Neuw84!
   
   This is the same classloader issue as #3737, fixed by #4609. The `Could not 
validate FileScanTasks: org.apache.iceberg.ContentScanTask` message is a 
`ClassNotFoundException`: `validateIcebergFileScanTasks` was still using 
single-arg `Class.forName`, which uses Comet's classloader rather than the 
thread context classloader. Since you load Iceberg via `spark.jars.packages` (a 
child application classloader) while the Comet jar is on the system classpath, 
the lookup fails and the scan falls back to Spark, which is why your numbers 
match vanilla Spark.
   
   #4609 swaps those calls to use the thread context classloader, but it landed 
after 0.16.0 was tagged, so it isn't in the release you're on.
   
   Could you try a snapshot build to confirm it resolves your case? As an 
immediate workaround, putting the Iceberg jars on the same classpath as the 
Comet jar (e.g. both in Spark's `jars/` folder instead of via 
`spark.jars.packages`) should also avoid the fallback.
   
   Otherwise, 0.17 should be available by the end of next week (tracking in 
#4564) and will include the fix.
   


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