It seems like when JVM reuse is enabled map task log data is not getting written to their corresponding log files; log data from certain map tasks gets appended to log files corresponding to some other map task.
For example, I have a case here where 8 map JVMs are running simultaneously and all syslog data from map task 9, 17 and 25 gets appended in to log file for map task 0. Whereas no syslog file gets generated in attempt_*m_000009_0/ , attempt_*m_000017_0/ and attempt_*m_000025_0/ folders. This job creates 32 map tasks. This behavior might also be applicable to reduce log files, however, in our case total # of reduce tasks is not more than max reduce JVMs running at the same time and hence it might not be manifesting. BTW, this is on Apache distro 0.21.0. -Shrinivas
