`git_add()` slow

[krlmlr]

These measurements surprised me:

dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
writeLines(character(), "a.txt")
system.time(gert::git_add("."))
#>    user  system elapsed 
#>   0.019   0.002   0.105
gert::git_commit(message = "Test")
#> [1] "b49672895dc220cb508a17b1b716558b9d11fb6a"

^{Created on 2024-11-16 with reprex v2.1.1}

Running git as an external process is much faster:

dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
writeLines(character(), "a.txt")
system.time(system("git add a.txt"))
#>    user  system elapsed 
#>   0.003   0.005   0.037
gert::git_commit(message = "Test")
#> [1] "521a3b6ee3e59e6990b37e6f61da3ed17c0fb623"

^{Created on 2024-11-16 with reprex v2.1.1}

git2r seems to have the same problems. What is libgit2 doing there?

The implementation seems to not use the results of normalizePath(), and 20 out of the 100 milliseconds are spent in git_status(), regardless if the caller cares about the result. Need to understand why R_git_repository_add is slow.

gert::git_add
#> function (files, force = FALSE, repo = ".") 
#> {
#>     repo <- git_open(repo)
#>     info <- git_info(repo)
#>     normalizePath(file.path(info$path, files), mustWork = FALSE)
#>     force <- as.logical(force)
#>     .Call(R_git_repository_add, repo, files, force)
#>     git_status(repo = repo)
#> }
#> <bytecode: 0x113181fa8>
#> <environment: namespace:gert>

^{Created on 2024-11-16 with reprex v2.1.1}

[jeroen]

Does the overhead get bigger when adding many files at once? Or is it a fixed overhead of 0.1sec?

[krlmlr]

There's a substantial cost per file. With 100 files, gert needs almost 6 seconds:

N <- 100

dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
for (i in 1:N) {
  writeLines(character(), paste0(i, ".txt"))
}
system.time(gert::git_add("."))
#>    user  system elapsed 
#>   0.013   0.047   5.499
nrow(gert::git_status())
#> [1] 100
gert::git_commit(message = "Test")
#> [1] "05e7dd6d0077f78dada74864b44866ae8fb8e976"


dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
for (i in 1:N) {
  writeLines(character(), paste0(i, ".txt"))
}
system.time(system2("git", args = c("add", ".")))
#>    user  system elapsed 
#>   0.003   0.007   0.025
nrow(gert::git_status())
#> [1] 100
gert::git_commit(message = "Test")
#> [1] "05e7dd6d0077f78dada74864b44866ae8fb8e976"

^{Created on 2024-11-16 with reprex v2.1.1}

[krlmlr]

I truly wonder why the commit hash comes out as the same in the first example. Does the commit hash uses the system time with accuracy to the second only?

Same timing (but different commit hashes) if I swap:

N <- 100

dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
for (i in 1:N) {
  writeLines(character(), paste0(i, ".txt"))
}
system.time(system2("git", args = c("add", ".")))
#>    user  system elapsed 
#>   0.004   0.007   0.039
nrow(gert::git_status())
#> [1] 100
gert::git_commit(message = "Test")
#> [1] "5eb64df18ee4bb3cc5371faf644833a23e04216c"

dir <- withr::local_tempdir()
setwd(dir)

gert::git_init()
for (i in 1:N) {
  writeLines(character(), paste0(i, ".txt"))
}
system.time(gert::git_add("."))
#>    user  system elapsed 
#>   0.011   0.043   5.014
nrow(gert::git_status())
#> [1] 100
gert::git_commit(message = "Test")
#> [1] "933c72ecc0ce1bd962fddbeb55b916e94abc1717"

^{Created on 2024-11-16 with reprex v2.1.1}