Hello! On Mon, Mar 26, 2018 at 08:21:27PM +0000, John Melom wrote:
> I am load testing our system using Jmeter as a load generator. > We execute a script consisting of an https request executing in > a loop. The loop does not contain a think time, since at this > point I am not trying to emulate a “real user”. I want to get a > quick look at our system capacity. Load on our system is > increased by increasing the number of Jmeter threads executing > our script. Each Jmeter thread references different data. > > Our system is in AWS with an ELB fronting Nginx, which serves as > a reverse proxy for our Docker Swarm application cluster. > > At moderate loads, a subset of our https requests start > experiencing to a 1 second delay in addition to their normal > response time. The delay is not due to resource contention. > System utilizations remain low. The response times cluster > around 4 values: 0 millilseconds, 50 milliseconds, 1 second, > and 1.050 seconds. Right now, I am most interested in > understanding and eliminating the 1 second delay that gives the > clusters at 1 second and 1.050 seconds. > > The attachment shows a response time scatterplot from one of our > runs. The x-axis is the number of seconds into the run, the > y-axis is the response time in milliseconds. The plotted data > shows the response time of requests at the time they occurred in > the run. > > If I run the test bypassing the ELB and Nginx, this delay does > not occur. > If I bypass the ELB, but include Nginx in the request path, the > delay returns. > > This leads me to believe the 1 second delay is coming from > Nginx. There are no magic 1 second delays in nginx - unless you've configured something explicitly. Most likely, the 1 second delay is coming from TCP retransmission timeout during connection establishment due to listen queue overflows. Check "netstat -s" to see if there are any listen queue overflows on your hosts. [...] -- Maxim Dounin http://mdounin.ru/ _______________________________________________ nginx mailing list [email protected] http://mailman.nginx.org/mailman/listinfo/nginx
