Unfortunately, the JDK doesn't have any option to append to existing log instead of overwriting so the latest log is overwritten. Maybe we can have the bin/solr script roll that after the process is killed?
We do backup the last gc log before we start? We probably can change that to roll to the same file name as what the JVM would have done.
That apart, this should probably keep this similar to log4j defaults, i.e. 4 MB, and 9 logs.
This probably also made me think about the way we are probably inconsistent with the number of logs and the log retention policy with the main Solr log. We currently ask log4j to retain 9 logs, but roll over to a timestamped file as well at startup – that will never be part of the retention policy..