A lot of time is spent in go-git.v4/config.RefSpec.matchExact

[jfontan]

When the repository has a lot of references a lot of time is spent comparing ref names.

(pprof) top
Showing nodes accounting for 28940ms, 96.47% of 30000ms total
Dropped 11 nodes (cum <= 150ms)
Showing top 10 nodes out of 24
      flat  flat%   sum%        cum   cum%
   11820ms 39.40% 39.40%    11820ms 39.40%  runtime.memeqbody /usr/lib/go-1.9/src/runtime/asm_amd64.s
    4750ms 15.83% 55.23%    28100ms 93.67%  github.com/src-d/borges/vendor/gopkg.in/src-d/go-git%2ev4.(*Remote).addReferenceIfRefSpecMatches /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/remote.go
    3280ms 10.93% 66.17%     3280ms 10.93%  runtime.indexbytebody /usr/lib/go-1.9/src/runtime/asm_amd64.s
    1850ms  6.17% 72.33%     4220ms 14.07%  github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config.RefSpec.Src /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config/refspec.go
    1720ms  5.73% 78.07%    29960ms 99.87%  github.com/src-d/borges/vendor/gopkg.in/src-d/go-git%2ev4.(*Remote).addOrUpdateReferences /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/remote.go
    1610ms  5.37% 83.43%     5690ms 18.97%  strings.Index /usr/lib/go-1.9/src/strings/strings_amd64.go
    1270ms  4.23% 87.67%    17560ms 58.53%  github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config.RefSpec.matchExact /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config/refspec.go
    1100ms  3.67% 91.33%    23330ms 77.77%  github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config.RefSpec.Match /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config/refspec.go
     800ms  2.67% 94.00%      800ms  2.67%  strings.IndexByte /usr/lib/go-1.9/src/runtime/asm_amd64.s
     740ms  2.47% 96.47%     4060ms 13.53%  strings.Contains /usr/lib/go-1.9/src/strings/strings.go
(pprof) list RefSpec.Match
Total: 30s
ROUTINE ======================== github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config.RefSpec.Match in /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config/refspec.go
     1.10s     23.33s (flat, cum) 77.77% of Total
         .          .     73:
         .          .     74:	return spec[start:end]
         .          .     75:}
         .          .     76:
         .          .     77:// Match match the given plumbing.ReferenceName against the source.
     210ms      210ms     78:func (s RefSpec) Match(n plumbing.ReferenceName) bool {
     430ms      5.10s     79:	if !s.IsWildcard() {
     430ms     17.99s     80:		return s.matchExact(n)
         .          .     81:	}
         .          .     82:
      30ms       30ms     83:	return s.matchGlob(n)
         .          .     84:}
         .          .     85:
         .          .     86:// IsWildcard returns true if the RefSpec contains a wildcard.
         .          .     87:func (s RefSpec) IsWildcard() bool {
         .          .     88:	return strings.Contains(string(s), refSpecWildcard)
(pprof) list RefSpec.matchExact
Total: 30s
ROUTINE ======================== github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config.RefSpec.matchExact in /root/go/src/github.com/src-d/borges/vendor/gopkg.in/src-d/go-git.v4/config/refspec.go
     1.27s     17.56s (flat, cum) 58.53% of Total
         .          .     86:// IsWildcard returns true if the RefSpec contains a wildcard.
         .          .     87:func (s RefSpec) IsWildcard() bool {
         .          .     88:	return strings.Contains(string(s), refSpecWildcard)
         .          .     89:}
         .          .     90:
     210ms      210ms     91:func (s RefSpec) matchExact(n plumbing.ReferenceName) bool {
     530ms      4.75s     92:	src := s.Src()
         .          .     93:	name := n.String()
     530ms     12.60s     94:	return src == name
         .          .     95:
         .          .     96:	// return s.Src() == n.String()
         .          .     97:}
         .          .     98:
         .          .     99:func (s RefSpec) matchGlob(n plumbing.ReferenceName) bool {

Most probably the method Remote.addOrUpdateReferences is called too much.

[jfontan]

This was addressed in src-d/go-git#833.