J2EE application performance QA and tuning (3)
Balancing Network Load with Priority Queues Tips:
- Hardware traffic managers redirect user requests to a farm of servers based on server availability, IP address, or port number. All traffic is routed to the load balancer, then requests are fanned out to servers based on the balancing algorithm.
- Popular load-balancing algorithms include: server availability (find a server with available processing capability); IP address management (route to the nearest server by IP address); port number (locate different types of servers on different machines, and route by port number); HTTP header checking (route by URI or cookie, etc).
- Web hits should cater for handling peak hit rate, not the average rate.
- You can model hit rates using gaussian distribution to determine the average hit rate per time unit (e.g. per second) at peak usage, then a poisson probability gives the probability of a given number of users simulatneously hitting the server within that time unit. [Article gives an example with gaussian fitted to peak traffic of 4000 users with a standard deviation of 20 minutes resulting in an average of 1.33 users per second at the peak, which in turn gives the probabilities that 0, 1, 2, 3, 4, 5, 6 users hitting the server within one second as 26%, 35%, 23%, 10%, 3%, 1%, 0.2%. Service time was 53 milliseconds, which means that the server can service 19 hits per second without the service rate requiring requests being queued.]
- System throughput is the arrival rate divided by the service rate. If the ratio becomes greater than one, requests exceed the system capability and will be lost or need to be queued.
- If requests are queued because capacity is exceeded, the throughput must drop sufficiently to handle the queued requests or the system will fail (the service rate must increase or arrival rate decrease). If the average throughput exceeds 1, then the system will fail.
- Sort incoming requests into different priority queues, and service the requests according to the priorities assigned to each queue.
For any detail, please contact email@example.com