git2graph

git2graph crawls a Git repository and outputs it as a graph, i.e., as a pair of textual files <nodes, edges>. The nodes file will contain a list of graph nodes as Software Heritage (SWH) Persistent Identifiers (SWHIDs); the edges file a list of graph edges as <from, to> SWHID pairs.

Dependencies

Build time dependencies:

Test dependencies:

Micro benchmark

$ time ./git2graph -n >(zstdmt > nodes.csv.zst) -e >(zstdmt -c > edges.csv.zst) /srv/src/linux
160,38s user 12,72s system 98% cpu 2:55,02 total

$ zstdcat nodes.csv.zst | wc -l
6503403
$ zstdcat edges.csv.zst | wc -l
305096029

Parallel use

git2graph writes fixed-length lines, long either 51 bytes (nodes) or 102 bytes (edges). When writing to a FIFO less than PIPE_BUF bytes (which is 4096 bytes on Linux, and guaranteed to be at least 512 bytes by POSIX), writes are atomic. Hence it is possible to mass analyze many repositories in parallel with something like:

$ mkfifo nodes.fifo edges.fifo
$ sort -u < nodes.fifo | zstdmt > nodes.csv.zst &
$ sort -u < edges.fifo | zstdmt > edges.csv.zst &
$ parallel git2graph -n nodes.fifo -e edges.fifo -- repo_dir_1 repo_dir_2 ...
$ rm nodes.fifo edges.fifo

Note that you most likely want to tune sort in order to be parallel (--parallel), use a large buffer size (-S), and use a temporary directory with enough available space (-T). (The above example uses parallel from moreutils, but it could trivially be adapted to use GNU parallel or similar parallelization tools.)

Limitations

Snapshot SWHID calculation is not fully compatible with the spec, because currently only HEAD is considered as a symbolic reference. Other symbolic refs, if present, will be ignored, potentially leading to a different snapshot SWHID than what Software Heritage will obtain. This is due to a limitation of libgit2, that at the time of writing doesn’t allow to list all symbolic references.

The graph structure is not affected, but looking up obtained snapshots by SWHID on the main Software Heritage archive might fail.