This depends on the configuration of syslog-ng, the hardware running syslog-ng, and the exact situation and environment. The limits of the throughput of syslog-ng are similar to the limits of other network applications. When sizing the hardware required for syslog-ng, try to estimate the log traffic to be processed and the filtering complexity to be applied.
The main limiting factors are the following:
Other limiting factors are:
For more details, check syslog-ng pe v5.0 performance whitepaper!