Explanation of Throttle Settings in LiteSpeed. How does the Throttle parameter affect the server during the LiteSpeed backup or restore processes?
The percentage value entered in LiteSpeed, for throttling, is the percentage of overall machine CPU utilization. It is not the usage percentage that LiteSpeed may consume on any given single CPU. Further, LiteSpeed does not exactly hard cap the usage at the specified value, but strives to maintain the specified usage as the running mean. Therefore at any time, usage may be slightly lower or higher until the next throttle correction occurs. There are no specific guarantees how this will affect any individual processor.
The throttling algorithm in 5.x is more adaptable than in previous versions- as it tries to maintain an overall average. This means that if other processes takes resources from LiteSpeed or I/O bandwidth is bottlenecking the CPU, the engine may increase its processing to make up for the previous idle time.
Notes to consider:
(1) Throttle is entirely separate from affinity. At any given throttle value an affinity setting can increase the CPU consumption on the allowed CPUs. Again, this is because throttle applies to the entire system - not just processors it will run on due to affinity.
(2) Overall CPU usage may be higher than expected as any backup/restore also has a component of work within SQL Server. LiteSpeed will not throttle a SQL Server service.
(3) CPU usage can be affected by other processes running within the system - especially any active processes running on the same CPU.
(4) CPU throttle characteristics are affected by various LiteSpeed settings such as affinity and thread count.
(5) Throttle affects only the engine instance of LiteSpeed to which it was applied. If multiple LiteSpeed processes are running, the sum of their combined CPU usagemay be more than any individual setting.
