Hello!
On Fri, Jul 11, 2014 at 5:44 AM, rvsw wrote:
> Will there be performance impact if systemtap is used on an nginx system
> handling traffic. As the requirements mention, we need kernel with userspace
> tracing plus dtrace enabled in the openresty code? I didn't find any clear
> documentation on if there is any performance degradation expected and if so,
> approximately how much
>
This highly depends on the actual tools being used and the
applications being analyzed (and even the actual traffic). You can
always measure the impact with tools like ab yourself, for example.
I've just added some notes regarding the impact on the *throughput
limit* to some of the tools' documentation. To quote,
sample-bt: "The overhead exposed on the target process is usually
small. For example, the throughput (req/sec) limit of an nginx worker
process doing simplest "hello world" requests drops by only 11% (only
when this tool is running), as measured by `ab -k -c2 -n100000` when
using Linux kernel 3.6.10 and systemtap 2.5. The impact on
full-fledged production processes is usually smaller than even that,
for instance, only 6% drop in the throughput limit is observed in a
production-level Lua CDN application."
lj-lua-stacks: "The overhead exposed on the target process is usually
small. For example, the throughput (req/sec) limit of an nginx worker
process doing simplest "hello world" requests drops by only 10% (only
when this tool is running), as measured by `ab -k -c2 -n100000` when
using Linux kernel 3.6.10 and systemtap 2.5. The impact on
full-fledged production processes is usually smaller than even that,
for instance, only 5% drop in the throughput limit is observed in a
production-level Lua CDN application."
ngx-lua-exec-time: "The overhead exposed on the target process is
usually small. For example, the throughput (req/sec) limit of an nginx
worker process running a full-fledged Lua CDN application drops by
only 14% (only when this tool is running), as measured by `ab -k -c2
-n100000` when using Linux kernel 3.6.10 and systemtap 2.5."
Best regards,
-agentzh
