Enabling logging on Apache causes performance problems

Hi,

We are using Apache v2.2.3 on a Redhat Enterprise Linux 5.6 with php 5.1.6 and mysql 5.0.77.
When enabling apache logs and customizing logging behavior by defining a CustomLog and a LogFormat in the apache's configuration file, apache hangs up.
We notice that we want to send Apache's log files to a syslog server.
We want to know what are sources of such as problem.

Thank you