housekeeping: Skip repacking empty repositories

When a repository does not have any bitmaps or in case it is missing
bloom filters in the commit graph we always try to do a full repack in
order to generate these data structures. This logic is required because:

    - Bitmaps are only generated by git-repack(1) for full repacks. This
      limitation exists because there can only be one bitmap per
      repository.

    - In case commit-graphs exist but missing bloom filters we need to
      completely rewrite them in order to enable this extension.

While the logic makes sense, it also causes us to repack repositories
which are empty: they don't contain either of these data structures, and
consequentially we think we need a full repack. While this is not a huge
problem because git-repack(1) would finish fast anyway in case the repo
doesn't contain any objects, we still needlessly spawn a process. Also,
our metrics report that we're doing a lot of full repacks, which can be
confusing.

Improve our heuristics by taking into account whether the repository has
objects at all. If there aren't any, we can avoid all this busywork and
just skip repacking altogether.

Changelog: changed

1 files changed, 6 insertions, 0 deletions

diff --git a/internal/gitaly/service/repository/optimize_test.go b/internal/gitaly/service/repository/optimize_test.go
index 0bc1932d5..a843b5668 100644
--- a/internal/gitaly/service/repository/optimize_test.go
+++ b/internal/gitaly/service/repository/optimize_test.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
@@ -107,6 +108,11 @@ func TestOptimizeRepository(t *testing.T) {
 		)
 	}
 
+	// Write a blob whose OID is known to have a "17" prefix, which is required such that
+	// OptimizeRepository would try to repack at all.
+	blobOIDWith17Prefix := gittest.WriteBlob(t, cfg, testRepoPath, []byte("32"))
+	require.True(t, strings.HasPrefix(blobOIDWith17Prefix.String(), "17"))
+
 	bitmaps, err := filepath.Glob(filepath.Join(testRepoPath, "objects", "pack", "*.bitmap"))
 	require.NoError(t, err)
 	require.Empty(t, bitmaps)