I have this log4j.xml configuration file: http://www.grupoventus.com/download/log4j.xml
There is an async logger called LOGGER_ACCESS that is using a RollingFileAppender named ACCESS_LOG.
We have sent an stress test against our application, about 500 simultaneous requests. Every request appends a new line to the current log.
At 00:00 log file was rotated, and now there are two logs (as expected): vproxy_acccess.2015-04-16 (the older) and vproxy_access (the current from today, day 17).
But if we take a look to the old log file, we see this. Below the last two lines of my log:
The first request from 2015-04-17 has been included into the log from day 16. Just the first one, the rest have been correctly appended to the vproxy_access log.