For informational or debug messages, use slapi_log_info_ex(). This function can be set for default logging, which means that the message is not logged when logging is turned off for plug-ins. Informational logging can also be set to occur only when heavy logging is used. Thus, the message is logged when plug-in logging is both turned on and set to log all informational messages.
Refer to Review the Plug-In for an example of how to log an informational message from a plug-in.