The direct (online) report generation utilizes more server CPU as it executes SQL commands directly on the server. Based on our experience, the CPU load on the publisher increases by 10% during the sync process. So, if the CPU is about 20% on a publisher during normal operations, the report generation increases the CPU load to 30%. This slight increase should have no business impact, but in some setups might be considered worth avoiding.
We have introduced SYNC MODE to sync the required data to a local data store. The processing impact on CUCM, CUC and CUPS is reduced to only the copying of data. Complex SQL commands are no longer processed on these Cisco servers, reducing the CPU usage compared to the direct (online) report generation. Do take into account that the sync process copies about 100 to 300 MB to the Windows machine.
Off-line report generation reduces CPU usage but increases network utilization. Off-line (sync) should be used in the LAN when a CPU increases are to be minimized. Direct (online) report generation should be used over WAN.
If the average CPU level is above 30% on the publisher (which we have hardly seen), it is recommended that reports be generated outside of business hours.