Excluding failed records from the CAS Service log file
If a record fails during a crawl, the CAS Server discards the failed record and writes a truncated version of the record to the cas-service.log file. If you do not want the CAS Server to write any information about failed records to the log file, you can disable logging for failed records by uncommenting a setting in the cas-service-log4j.properties file.
Enabling log timing information for crawl processing steps
You can enable a logging setting in cas-service-log4j.properties that instructs CAS to write log timing information for each processing step of a crawl. This additional logging information is especially useful for troubleshooting performance issues.