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fetchGit: use a better caching scheme

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The current usage technically works by putting multiple different
repos in to the same git directory. However, it is very slow as
Git tries very hard to find common commits between the two
repositories. If the two repositories are large (like Nixpkgs and
another long-running project,) it is maddeningly slow.

This change busts the cache for existing deployments, but users
will be promptly repaid in per-repository performance.
This commit is contained in:
Graham Christensen 2018-08-17 10:29:32 -04:00
parent d277442df5
commit 02098d2073
2 changed files with 5 additions and 3 deletions
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4
src/libexpr/primops/fetchGit.cc
View file

@ -3,6 +3,7 @@
#include "download.hh"
#include "store-api.hh"
#include "pathlocks.hh"
#include "hash.hh"
#include <sys/time.h>
@ -84,9 +85,10 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
if (rev != "" && !std::regex_match(rev, revRegex))
throw Error("invalid Git revision '%s'", rev);
Path cacheDir = getCacheDir() + "/nix/git";
Path cacheDir = getCacheDir() + "/nix/gitv2/" + hashString(htSHA256, uri).to_string(Base32, false);
if (!pathExists(cacheDir)) {
createDirs(dirOf(cacheDir));
runProgram("git", true, { "init", "--bare", cacheDir });
}

4
tests/fetchGit.sh
View file

@ -9,7 +9,7 @@ clearStore
repo=$TEST_ROOT/git
rm -rf $repo ${repo}-tmp $TEST_HOME/.cache/nix/git
rm -rf $repo ${repo}-tmp $TEST_HOME/.cache/nix/gitv2
git init $repo
git -C $repo config user.email "foobar@example.com"
@ -129,7 +129,7 @@ path5=$(nix eval --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outP
# Nuke the cache
rm -rf $TEST_HOME/.cache/nix/git
rm -rf $TEST_HOME/.cache/nix/gitv2
# Try again, but without 'git' on PATH
NIX=$(command -v nix)