On Sun, 4 Dec 2016 09:17:00 -0500 Patrick Hemmer <[email protected]> wrote:
> I was mostly just wondering about differences between using things like > `capture request header`/`http-request capture` and `http-request set-var`. > > set-var seems to have all the capabilities of captures, and are much > easier to work with. You don't have to pre-declare them, you don't have > to set their size, you don't have to remember the order in which you > declared them and reference them by an index. > > So what's the benefit of captures? Are they more performant or something? Hi Patrick, This is a good question ! Capture header are faster. It uses memory pool of predefined size and the access to a captures header is fast because it is indexed with an integer. set-var uses the standard system memory allocation and a memory accounting system for preventing a large amount of consomation. This memory allocation system is slow. In other way, each is stored in a list and HAProxy must browse this list for each var access. So, you're right: capture header is more performant. set-var is more easy to use. Note that the var cotaining ip or integer doesn't use the system memory allocator. Finally, I realize a quick benchmark on my computer. I capture the header user-agent containing 127 bytes (and configured for capturing 128) with the two methods. set-var : 90262 req/s capture : 92257 req/s So, on my computer, "set-var" is 2% slowly than "capture". Thierry
