How to know the name(url) of documents that data import handler skipped

[Yasufumi Mizoguchi]

Hi,

I am trying to indexing files into Solr 7.2 using data import handler with
onError=skip option.
But, I am struggling with determining the skipped documents as logs do not
tell which file was bad.
So, how can I know those files?

Thanks,
Yasufumi