2 Debian Code Search: An Overview

4 Search result quality
4.11 Performance by processing step (profiling)
When optimizing software, the first step is to profile the software to see which part of it is
actually slow. This is important because intuitively, one might have an entirely different part
in mind, for example an algorithm which has some potential for optimization, while there
are many other low-hanging fruit which can yield even greater performance improvements.
To profile which parts of Debian Code Search are slow, additional parameters have been
added to dcs-web, just like in section 4.10.1. Since the code is so simple, the additional
measurements do not influence the performance itself in any noticeable way:
func Search(w http.ResponseWriter , r *http.Request) {
var t0, t1 time.Time
t0 = time.Now()
// ... send request to index -backend ...
t1 = time.Now()
// ...
w.Header().Add("dcs -t0", fmt.Sprintf("%.2fms",
float32(t1.Sub(t0).Nanoseconds())/1000/1000))
}
4.11.1 Before any optimization
Figure 4.10 shows that a substantial amount of time is used for the trigram index lookup:
It takes about 40 ms until the first result appears. Note that results are ranked as they are
received, so the “ranking” step covers receiving and ranking the files.
response time
100 ms
80 ms
60 ms
40 ms
20 ms
0 ms
Response split into steps
0 20 40 60 80 100
total time
grep
request
sorting
ranking
n-gram
Figure 4.10: The trigram index lookup (“n-gram”) took almost as long as the actual searching
of files containing possible matches (“grep”) before optimization.
52