measuring lua execution time only (not ngx.var.request_time)

pavel.zhuk · 2016-10-28T20:41:36+00:00

Have you looked at https://github.com/openresty/lua-resty-core/blob/master/lib/ngx/ssl.md ?On Thursday, October 27, 2016 at 3:48:36 PM UTC-4, Allan Mor...

measuring lua execution time only (not ngx.var.request_time)

pavel.zhuk

Hi,

I am trying to measure response latency of some lua code running in production, and so I tried to analyze ngx.var.request_time values.
However, ngx.var.request_time seems to be calculated as total request handling time, which includes a time of I/O operations like response delivery to the client as well as LUA code execution time.
In my case, some of the responses could be quite slow due to low network performance of the clients (mobiles), and so my statistic figures are affected by actual client behavior very much.

So my question - is there any good way to get a request handling time, excluding a time spent on client related I/O ?

Thanks

BR,
Pavlo

rpaprocki

Hi,

On Fri, Oct 28, 2016 at 5:41 AM, Pavlo Zhuk <pave...@gmail.com> wrote:

Hi,

I am trying to measure response latency of some lua code running in production, and so I tried to analyze ngx.var.request_time values.
However, ngx.var.request_time seems to be calculated as total request handling time, which includes a time of I/O operations like response delivery to the client as well as LUA code execution time.
In my case, some of the responses could be quite slow due to low network performance of the clients (mobiles), and so my statistic figures are affected by actual client behavior very much.

So my question - is there any good way to get a request handling time, excluding a time spent on client related I/O ?

Yes, there are a handful of options, depending on your exact needs and use case:

- Lower level tracing can be done via https://github.com/openresty/stapxx#ngx-lua-exec-time (see also https://github.com/openresty/nginx-systemtap-toolkit)

- High granularity (micro- or nano-second precision) can be achieved with a little manual FFI work: https://www.cryptobells.com/openresty-time-resolution-with-ffi-a-more-accurate-approach/

- Second or microsecond precision can be achieved simply by storing the contents of ngx.now()/ngx.time() at the beginning of your Lua work, and calling ngx.update_time() and comparing the result of a separate ngx.now()/ngx.time() call to the first variable.

Good luck with it!