Log4cxx performance has been improved by the last 2 releases, Release 1.3.0 significantly reduced the overhead of sending events to the appender and release 1.2.0 reduced the frequency of mutex contention when sending envents to the appender.

Log4cxx can not guarantee entries in the log file are in the order in which logging requests are generated. The timestamp indicates the time the request was generated (i.e. when the LOG4CXX_INFO macro was executed). The operating system scheduler may suspend a thread between LoggingEvent creation and the system call that adds to the log file.

AsyncAppender has been extensively overhaulled in release 1.3.0 to improve thoughput when logging from multiple threads (see the times in example benchmarks)