Trace File Location For a Concurrent Request

For concurrent program

Get the request id of concurrent request, Run following sql to get trace filename and directory

  SELECT dump.value dir
       , dbname.value || '_ora_' || oracle_process_id || '.trc' filename
    FROM v$parameter                  dbname
       , v$parameter                  dump
       , apps.fnd_concurrent_requests req
   WHERE request_id  = :request_id
     AND dbname.name = 'db_name'
     AND dump.name   = 'user_dump_dest'

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More detail can be found at this Metalink Note 453527.1