Configuring Jetty for highload, albeit for load testing or for production, requires that the operating system, the JVM, jetty, the application, the network and the load generation all be tuned.
Load Generation for Load Testing
- The load generation machines must have their OS, JVM etc tuned just as much as the server machines.
- The load generation should not be over the local network on the server machine, as this has unrealistic performance and latency as well as different packet sizes and transport characteristics.
- The load generator should generate a realistic load:
- A common mistake is that load generators often open relatively few connections that are kept totally busy sending as many requests as possible over each connection. This causes the measured throughput to be limited by request latency (see Lies Damned Lies and Benchmarks for an analysis of such an issue.
- Another common mistake is to use a TCP/IP for a single request and to open many many short lived connections. This will often result in accept queues filling and limitations due to file descriptor and/or port starvation.
- A load generator should well model the traffic profile from the normal clients of the server. For browsers, this if mostly between 2 and 6 connections that are mostly idle and that are used in sporadic bursts with read times in between. The connections are mostly long held HTTP/1.1 connections.
- Load generators should be written in asynchronous programming style, so that limited threads does not limit the maximum number of users that can be simulated. If the generator is not asynchronous, then a thread pool of 2000 may only be able to simulate 500 or less users. The Jetty HttpClient is an ideal basis for building a load generator, as it is asynchronous and can be used to simulate many thousands of connections (see the Cometd Load Tester for a good example of a realistic load generator).
Operating System Tuning
Both the server machine and any load generating machines need to be tuned to support many TCP/IP connections and high throughput.
Linux does a reasonable job of self configuring TCP/IP, but there are a few limits and defaults that that are best increased. These can mostly be configured in /etc/security/limits.conf or via sysctl
TCP Buffer Sizes
These should be increased to at least 16MB for 10G paths and tune the autotuning (although buffer bloat now needs to be considered).
sysctl -w net.core.rmem_max = 16777216 sysctl -w net.core.wmem_max = 16777216 sysctl -w net.ipv4.tcp_rmem = 4096 87380 16777216 sysctl -w net.ipv4.tcp_wmem = 4096 65536 16777216
Linux supports pluggable congestion control algorithms. To get a list of congestion control algorithms that are available in your kernel run:
If cubic and/or htcp are not listed then you will need to research the control algorithms for your kernel. You can try setting the control to cubic with:
sysctl -w net.ipv4.tcp_congestion_control=cubic
Low Resource Limits