Merge branch 'pks-housekeeping-write-multi-pack-index' into 'master'

housekeeping: Enable writing of multi-pack-indices

Closes #2661

See merge request https://gitlab.com/gitlab-org/gitaly/-/merge_requests/5275

Merged-by: Patrick Steinhardt <psteinhardt@gitlab.com>
Approved-by: Will Chandler <wchandler@gitlab.com>
Approved-by: Justin Tobler <jtobler@gitlab.com>
Reviewed-by: Patrick Steinhardt <psteinhardt@gitlab.com>
Reviewed-by: Will Chandler <wchandler@gitlab.com>

9 files changed, 474 insertions, 127 deletions

diff --git a/internal/git/housekeeping/optimization_strategy.go b/internal/git/housekeeping/optimization_strategy.go
index e1c7df86b..4fe51a863 100644
--- a/internal/git/housekeeping/optimization_strategy.go
+++ b/internal/git/housekeeping/optimization_strategy.go
@@ -5,6 +5,7 @@ import (
 	"math"
 
 	"gitlab.com/gitlab-org/gitaly/v15/internal/git/stats"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/metadata/featureflag"
 )
 
 // OptimizationStrategy is an interface to determine which parts of a repository should be
@@ -42,7 +43,7 @@ func NewHeuristicalOptimizationStrategy(info stats.RepositoryInfo) HeuristicalOp
 // ShouldRepackObjects checks whether the repository's objects need to be repacked. This uses a
 // set of heuristics that scales with the size of the object database: the larger the repository,
 // the less frequent does it get a full repack.
-func (s HeuristicalOptimizationStrategy) ShouldRepackObjects(context.Context) (bool, RepackObjectsConfig) {
+func (s HeuristicalOptimizationStrategy) ShouldRepackObjects(ctx context.Context) (bool, RepackObjectsConfig) {
 	// If there are neither packfiles nor loose objects in this repository then there is no need
 	// to repack anything.
 	if s.info.Packfiles.Count == 0 && s.info.LooseObjects.Count == 0 {
@@ -59,7 +60,12 @@ func (s HeuristicalOptimizationStrategy) ShouldRepackObjects(context.Context) (b
 	// a bitmap on their own. We do not yet use multi-pack indices, and in that case Git can
 	// only use one bitmap. We already generate this bitmap in the pool, so member of it
 	// shouldn't have another bitmap on their own.
-	if !s.info.Packfiles.Bitmap.Exists && len(s.info.Alternates) == 0 {
+	//
+	// Addendum: this isn't true anymore as we're rolling out multi-pack-indices. For one, they
+	// allow us to have bitmaps even in repositories that are linked via alternates. And second,
+	// they don't require a full repack in order to write the bitmap. So once we have fully
+	// rolled out multi-pack-indices this whole condition can go away.
+	if featureflag.WriteMultiPackIndex.IsDisabled(ctx) && !s.info.Packfiles.Bitmap.Exists && len(s.info.Alternates) == 0 {
 		return true, RepackObjectsConfig{
 			FullRepack:  true,
 			WriteBitmap: true,
@@ -107,8 +113,9 @@ func (s HeuristicalOptimizationStrategy) ShouldRepackObjects(context.Context) (b
 	if uint64(math.Max(lowerLimit,
 		math.Log(float64(s.info.Packfiles.Size/1024/1024))/math.Log(log))) <= s.info.Packfiles.Count {
 		return true, RepackObjectsConfig{
-			FullRepack:  true,
-			WriteBitmap: len(s.info.Alternates) == 0,
+			FullRepack:          true,
+			WriteBitmap:         len(s.info.Alternates) == 0 || featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+			WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 		}
 	}
 
@@ -127,8 +134,19 @@ func (s HeuristicalOptimizationStrategy) ShouldRepackObjects(context.Context) (b
 	// it is necessary on the client side. We thus take a much stricter limit of 1024 objects.
 	if s.info.LooseObjects.Count > looseObjectLimit {
 		return true, RepackObjectsConfig{
-			FullRepack:  false,
-			WriteBitmap: false,
+			FullRepack:          false,
+			WriteBitmap:         featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+			WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+		}
+	}
+
+	// In case both packfiles and loose objects are in a good state, but we don't yet have a
+	// multi-pack-index we perform an incremental repack to generate one.
+	if featureflag.WriteMultiPackIndex.IsEnabled(ctx) && !s.info.Packfiles.HasMultiPackIndex {
+		return true, RepackObjectsConfig{
+			FullRepack:          false,
+			WriteBitmap:         true,
+			WriteMultiPackIndex: true,
 		}
 	}
 
@@ -246,10 +264,11 @@ func NewEagerOptimizationStrategy(info stats.RepositoryInfo) EagerOptimizationSt
 // ShouldRepackObjects always instructs the caller to repack objects. The strategy will always be to
 // repack all objects into a single packfile. The bitmap will be written in case the repository does
 // not have any alterantes.
-func (s EagerOptimizationStrategy) ShouldRepackObjects(context.Context) (bool, RepackObjectsConfig) {
+func (s EagerOptimizationStrategy) ShouldRepackObjects(ctx context.Context) (bool, RepackObjectsConfig) {
 	return true, RepackObjectsConfig{
-		FullRepack:  true,
-		WriteBitmap: len(s.info.Alternates) == 0,
+		FullRepack:          true,
+		WriteBitmap:         len(s.info.Alternates) == 0 || featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+		WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 	}
 }
 
diff --git a/internal/git/housekeeping/optimization_strategy_test.go b/internal/git/housekeeping/optimization_strategy_test.go
index 405b3de84..b1ba6cc54 100644
--- a/internal/git/housekeeping/optimization_strategy_test.go
+++ b/internal/git/housekeeping/optimization_strategy_test.go
@@ -7,13 +7,17 @@ import (
 
 	"github.com/stretchr/testify/require"
 	"gitlab.com/gitlab-org/gitaly/v15/internal/git/stats"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/metadata/featureflag"
 	"gitlab.com/gitlab-org/gitaly/v15/internal/testhelper"
 )
 
 func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 	t.Parallel()
+	testhelper.NewFeatureSets(featureflag.WriteMultiPackIndex).Run(t, testHeuristicalOptimizationStrategyShouldRepackObjects)
+}
 
-	ctx := testhelper.Context(t)
+func testHeuristicalOptimizationStrategyShouldRepackObjects(t *testing.T, ctx context.Context) {
+	t.Parallel()
 
 	for _, tc := range []struct {
 		desc           string
@@ -40,8 +44,9 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 			},
 			expectedNeeded: true,
 			expectedConfig: RepackObjectsConfig{
-				FullRepack:  true,
-				WriteBitmap: true,
+				FullRepack:          featureflag.WriteMultiPackIndex.IsDisabled(ctx),
+				WriteBitmap:         true,
+				WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 			},
 		},
 		{
@@ -60,10 +65,23 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 			// If we have no bitmap in the repository we'd normally want to fully repack
 			// the repository. But because we have an alternates file we know that the
 			// repository must not have a bitmap anyway, so we can skip the repack here.
-			expectedNeeded: false,
+			//
+			// This changes though with multi-pack-indices, which allow for bitmaps to
+			// exist in pooled repositories.
+			expectedNeeded: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+			expectedConfig: func() RepackObjectsConfig {
+				if featureflag.WriteMultiPackIndex.IsEnabled(ctx) {
+					return RepackObjectsConfig{
+						WriteBitmap:         true,
+						WriteMultiPackIndex: true,
+					}
+				}
+
+				return RepackObjectsConfig{}
+			}(),
 		},
 		{
-			desc: "no repack needed",
+			desc: "no repack needed without multi-pack-index",
 			strategy: HeuristicalOptimizationStrategy{
 				info: stats.RepositoryInfo{
 					Packfiles: stats.PackfilesInfo{
@@ -74,7 +92,41 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 					},
 				},
 			},
-			expectedNeeded: false,
+			expectedNeeded: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+			expectedConfig: func() RepackObjectsConfig {
+				if featureflag.WriteMultiPackIndex.IsEnabled(ctx) {
+					return RepackObjectsConfig{
+						FullRepack:          false,
+						WriteBitmap:         true,
+						WriteMultiPackIndex: true,
+					}
+				}
+
+				return RepackObjectsConfig{}
+			}(),
+		},
+		{
+			desc: "no repack needed with multi-pack-index",
+			strategy: HeuristicalOptimizationStrategy{
+				info: stats.RepositoryInfo{
+					Packfiles: stats.PackfilesInfo{
+						Count:             1,
+						HasMultiPackIndex: true,
+					},
+				},
+			},
+			expectedNeeded: featureflag.WriteMultiPackIndex.IsDisabled(ctx),
+			expectedConfig: func() RepackObjectsConfig {
+				if featureflag.WriteMultiPackIndex.IsDisabled(ctx) {
+					return RepackObjectsConfig{
+						FullRepack:          true,
+						WriteBitmap:         true,
+						WriteMultiPackIndex: false,
+					}
+				}
+
+				return RepackObjectsConfig{}
+			}(),
 		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
@@ -159,6 +211,7 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 								Bitmap: stats.BitmapInfo{
 									Exists: true,
 								},
+								HasMultiPackIndex: true,
 							},
 							Alternates: tc.alternates,
 						},
@@ -174,8 +227,9 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 					repackNeeded, repackCfg := strategy.ShouldRepackObjects(ctx)
 					require.True(t, repackNeeded)
 					require.Equal(t, RepackObjectsConfig{
-						FullRepack:  true,
-						WriteBitmap: len(tc.alternates) == 0,
+						FullRepack:          true,
+						WriteBitmap:         len(tc.alternates) == 0 || featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+						WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 					}, repackCfg)
 				})
 			}
@@ -234,6 +288,7 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 							Bitmap: stats.BitmapInfo{
 								Exists: true,
 							},
+							HasMultiPackIndex: true,
 						},
 					},
 				}
@@ -241,8 +296,9 @@ func TestHeuristicalOptimizationStrategy_ShouldRepackObjects(t *testing.T) {
 				repackNeeded, repackCfg := strategy.ShouldRepackObjects(ctx)
 				require.Equal(t, outerTC.expectedRepack, repackNeeded)
 				require.Equal(t, RepackObjectsConfig{
-					FullRepack:  false,
-					WriteBitmap: false,
+					FullRepack:          false,
+					WriteBitmap:         repackNeeded && featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+					WriteMultiPackIndex: repackNeeded && featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 				}, repackCfg)
 			})
 		}
@@ -527,8 +583,11 @@ func TestHeuristicalOptimizationStrategy_NeedsWriteCommitGraph(t *testing.T) {
 
 func TestEagerOptimizationStrategy(t *testing.T) {
 	t.Parallel()
+	testhelper.NewFeatureSets(featureflag.WriteMultiPackIndex).Run(t, testEagerOptimizationStrategy)
+}
 
-	ctx := testhelper.Context(t)
+func testEagerOptimizationStrategy(t *testing.T, ctx context.Context) {
+	t.Parallel()
 
 	for _, tc := range []struct {
 		desc                     string
@@ -548,6 +607,7 @@ func TestEagerOptimizationStrategy(t *testing.T) {
 					Alternates: []string{"path/to/alternate"},
 				},
 			},
+			expectWriteBitmap:        featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 			expectShouldPruneObjects: true,
 		},
 		{
@@ -557,7 +617,8 @@ func TestEagerOptimizationStrategy(t *testing.T) {
 					IsObjectPool: true,
 				},
 			},
-			expectWriteBitmap: true,
+			expectWriteBitmap:        true,
+			expectShouldPruneObjects: false,
 		},
 		{
 			desc: "object pool with alternate",
@@ -567,14 +628,17 @@ func TestEagerOptimizationStrategy(t *testing.T) {
 					Alternates:   []string{"path/to/alternate"},
 				},
 			},
+			expectWriteBitmap:        featureflag.WriteMultiPackIndex.IsEnabled(ctx),
+			expectShouldPruneObjects: false,
 		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
 			shouldRepackObjects, repackObjectsCfg := tc.strategy.ShouldRepackObjects(ctx)
 			require.True(t, shouldRepackObjects)
 			require.Equal(t, RepackObjectsConfig{
-				FullRepack:  true,
-				WriteBitmap: tc.expectWriteBitmap,
+				FullRepack:          true,
+				WriteBitmap:         tc.expectWriteBitmap,
+				WriteMultiPackIndex: featureflag.WriteMultiPackIndex.IsEnabled(ctx),
 			}, repackObjectsCfg)
 
 			shouldWriteCommitGraph, writeCommitGraphCfg := tc.strategy.ShouldWriteCommitGraph(ctx)
diff --git a/internal/git/housekeeping/optimize_repository.go b/internal/git/housekeeping/optimize_repository.go
index 1238e74f7..4d9d5e50a 100644
--- a/internal/git/housekeeping/optimize_repository.go
+++ b/internal/git/housekeeping/optimize_repository.go
@@ -152,6 +152,7 @@ func optimizeRepository(
 		optimizations["packed_objects_full"] = "failure"
 		optimizations["packed_objects_incremental"] = "failure"
 		optimizations["written_bitmap"] = "failure"
+		optimizations["written_multi_pack_index"] = "failure"
 		return fmt.Errorf("could not repack: %w", err)
 	}
 	if didRepack {
@@ -163,6 +164,9 @@ func optimizeRepository(
 		if repackCfg.WriteBitmap {
 			optimizations["written_bitmap"] = "success"
 		}
+		if repackCfg.WriteMultiPackIndex {
+			optimizations["written_multi_pack_index"] = "success"
+		}
 	}
 	timer.ObserveDuration()
 
diff --git a/internal/git/housekeeping/optimize_repository_ext_test.go b/internal/git/housekeeping/optimize_repository_ext_test.go
index a956afb9d..087cf2fc1 100644
--- a/internal/git/housekeeping/optimize_repository_ext_test.go
+++ b/internal/git/housekeeping/optimize_repository_ext_test.go
@@ -25,7 +25,10 @@ import (
 
 func TestPruneIfNeeded(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testPruneIfNeeded)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testPruneIfNeeded)
 }
 
 func testPruneIfNeeded(t *testing.T, ctx context.Context) {
@@ -34,6 +37,13 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 	cfg := testcfg.Build(t)
 	cfg.SocketPath = testserver.RunGitalyServer(t, cfg, nil, setup.RegisterAll)
 
+	midxEnabledOrDisabled := func(enabled, disabled map[string]string) map[string]string {
+		if featureflag.WriteMultiPackIndex.IsEnabled(ctx) {
+			return enabled
+		}
+		return disabled
+	}
+
 	for _, tc := range []struct {
 		desc               string
 		isPool             bool
@@ -51,20 +61,34 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 			looseObjects: []string{
 				filepath.Join("ab/12345"),
 			},
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 		{
 			desc: "object in 17 shard",
 			looseObjects: []string{
 				filepath.Join("17/12345"),
 			},
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 		{
 			desc: "objects in different shards",
@@ -74,10 +98,17 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 				filepath.Join("12/12345"),
 				filepath.Join("17/12345"),
 			},
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 		{
 			desc:   "exceeding boundary on pool",
@@ -93,10 +124,17 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 
 				return looseObjects
 			}(),
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 		{
 			desc: "on boundary shouldn't prune",
@@ -115,10 +153,17 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 				t := time.Now().Add(stats.StaleObjectsGracePeriod).Add(-1 * time.Minute)
 				return &t
 			}(),
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 		{
 			desc: "exceeding boundary should prune",
@@ -137,11 +182,19 @@ func testPruneIfNeeded(t *testing.T, ctx context.Context) {
 				t := time.Now().Add(stats.StaleObjectsGracePeriod).Add(-1 * time.Minute)
 				return &t
 			}(),
-			expectedLogEntries: map[string]string{
-				"packed_objects_full": "success",
-				"pruned_objects":      "success",
-				"written_bitmap":      "success",
-			},
+			expectedLogEntries: midxEnabledOrDisabled(
+				map[string]string{
+					"packed_objects_incremental": "success",
+					"pruned_objects":             "success",
+					"written_bitmap":             "success",
+					"written_multi_pack_index":   "success",
+				},
+				map[string]string{
+					"packed_objects_full": "success",
+					"pruned_objects":      "success",
+					"written_bitmap":      "success",
+				},
+			),
 		},
 	} {
 		tc := tc
diff --git a/internal/git/housekeeping/optimize_repository_test.go b/internal/git/housekeeping/optimize_repository_test.go
index caddf732b..c13f08ead 100644
--- a/internal/git/housekeeping/optimize_repository_test.go
+++ b/internal/git/housekeeping/optimize_repository_test.go
@@ -28,7 +28,10 @@ import (
 
 func TestRepackIfNeeded(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testRepackIfNeeded)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testRepackIfNeeded)
 }
 
 func testRepackIfNeeded(t *testing.T, ctx context.Context) {
@@ -154,7 +157,10 @@ func TestPackRefsIfNeeded(t *testing.T) {
 
 func TestOptimizeRepository(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testOptimizeRepository)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testOptimizeRepository)
 }
 
 func testOptimizeRepository(t *testing.T, ctx context.Context) {
@@ -163,12 +169,24 @@ func testOptimizeRepository(t *testing.T, ctx context.Context) {
 	cfg := testcfg.Build(t)
 	txManager := transaction.NewManager(cfg, backchannel.NewRegistry())
 
+	type metric struct {
+		name, status string
+		count        int
+	}
+
+	midxEnabledOrDisabled := func(enabled, disabled []metric) []metric {
+		if featureflag.WriteMultiPackIndex.IsEnabled(ctx) {
+			return enabled
+		}
+		return disabled
+	}
+
 	for _, tc := range []struct {
 		desc                   string
 		setup                  func(t *testing.T, relativePath string) *gitalypb.Repository
 		expectedErr            error
-		expectedMetrics        string
-		expectedMetricsForPool string
+		expectedMetrics        []metric
+		expectedMetricsForPool []metric
 	}{
 		{
 			desc: "empty repository does nothing",
@@ -179,10 +197,9 @@ func testOptimizeRepository(t *testing.T, ctx context.Context) {
 				})
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: []metric{
+				{name: "total", status: "success", count: 1},
+			},
 		},
 		{
 			desc: "repository without bitmap repacks objects",
@@ -194,13 +211,21 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 				gittest.WriteCommit(t, cfg, repoPath, gittest.WithBranch("main"))
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_objects_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_bitmap", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_full", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "repository without commit-graph writes commit-graph",
@@ -213,11 +238,19 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 				gittest.Exec(t, cfg, "-C", repoPath, "repack", "-A", "-d", "--write-bitmap-index")
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "repository with commit-graph without generation data writes commit-graph",
@@ -231,11 +264,44 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 				gittest.Exec(t, cfg, "-c", "commitGraph.generationVersion=1", "-C", repoPath, "commit-graph", "write", "--split", "--changed-paths")
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
+		},
+		{
+			desc: "repository without multi-pack-index performs incremental repack",
+			setup: func(t *testing.T, relativePath string) *gitalypb.Repository {
+				repo, repoPath := gittest.CreateRepository(t, ctx, cfg, gittest.CreateRepositoryConfig{
+					SkipCreationViaService: true,
+					RelativePath:           relativePath,
+				})
+				gittest.WriteCommit(t, cfg, repoPath, gittest.WithBranch("main"))
+				gittest.Exec(t, cfg, "-C", repoPath, "repack", "-A", "-d", "-b")
+				return repo
+			},
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "repository with multiple packfiles packs only for object pool",
@@ -257,17 +323,33 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
-			expectedMetricsForPool: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_objects_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_bitmap", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "total", status: "success", count: 1},
+				},
+			),
+			expectedMetricsForPool: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "well-packed repository does not optimize",
@@ -281,10 +363,42 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 				gittest.Exec(t, cfg, "-c", "commitGraph.generationVersion=2", "-C", repoPath, "commit-graph", "write", "--split", "--changed-paths")
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "total", status: "success", count: 1},
+				},
+			),
+		},
+		{
+			desc: "well-packed repository with multi-pack-index does not optimize",
+			setup: func(t *testing.T, relativePath string) *gitalypb.Repository {
+				repo, repoPath := gittest.CreateRepository(t, ctx, cfg, gittest.CreateRepositoryConfig{
+					SkipCreationViaService: true,
+					RelativePath:           relativePath,
+				})
+				gittest.WriteCommit(t, cfg, repoPath, gittest.WithBranch("main"))
+				gittest.Exec(t, cfg, "-C", repoPath, "repack", "-A", "-d", "--write-bitmap-index", "--write-midx")
+				gittest.Exec(t, cfg, "-c", "commitGraph.generationVersion=2", "-C", repoPath, "commit-graph", "write", "--split", "--changed-paths")
+				return repo
+			},
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "recent loose objects don't get pruned",
@@ -314,12 +428,20 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_objects_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "old loose objects get pruned",
@@ -346,20 +468,37 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_objects_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_full", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="pruned_objects",status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "pruned_objects", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_commit_graph_full", status: "success", count: 1},
+					{name: "pruned_objects", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 			// Object pools never prune objects.
-			expectedMetricsForPool: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_objects_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="written_commit_graph_incremental", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetricsForPool: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 		{
 			desc: "loose refs get packed",
@@ -378,11 +517,20 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 
 				return repo
 			},
-			expectedMetrics: `# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository
-# TYPE gitaly_housekeeping_tasks_total counter
-gitaly_housekeeping_tasks_total{housekeeping_task="packed_refs", status="success"} 1
-gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
-`,
+			expectedMetrics: midxEnabledOrDisabled(
+				[]metric{
+					{name: "packed_objects_incremental", status: "success", count: 1},
+					{name: "packed_refs", status: "success", count: 1},
+					{name: "written_commit_graph_incremental", status: "success", count: 1},
+					{name: "written_bitmap", status: "success", count: 1},
+					{name: "written_multi_pack_index", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+				[]metric{
+					{name: "packed_refs", status: "success", count: 1},
+					{name: "total", status: "success", count: 1},
+				},
+			),
 		},
 	} {
 		tc := tc
@@ -399,14 +547,26 @@ gitaly_housekeeping_tasks_total{housekeeping_task="total", status="success"} 1
 			require.Equal(t, tc.expectedErr, err)
 
 			expectedMetrics := tc.expectedMetrics
-			if stats.IsPoolRepository(repoProto) && tc.expectedMetricsForPool != "" {
+			if stats.IsPoolRepository(repoProto) && tc.expectedMetricsForPool != nil {
 				expectedMetrics = tc.expectedMetricsForPool
 			}
 
+			var buf bytes.Buffer
+			_, err = buf.WriteString("# HELP gitaly_housekeeping_tasks_total Total number of housekeeping tasks performed in the repository\n")
+			require.NoError(t, err)
+			_, err = buf.WriteString("# TYPE gitaly_housekeeping_tasks_total counter\n")
+			require.NoError(t, err)
+
+			for _, metric := range expectedMetrics {
+				_, err := buf.WriteString(fmt.Sprintf(
+					"gitaly_housekeeping_tasks_total{housekeeping_task=%q, status=%q} %d\n",
+					metric.name, metric.status, metric.count,
+				))
+				require.NoError(t, err)
+			}
+
 			require.NoError(t, testutil.CollectAndCompare(
-				manager.tasksTotal,
-				bytes.NewBufferString(expectedMetrics),
-				"gitaly_housekeeping_tasks_total",
+				manager.tasksTotal, &buf, "gitaly_housekeeping_tasks_total",
 			))
 		})
 	}
diff --git a/internal/git/objectpool/fetch_test.go b/internal/git/objectpool/fetch_test.go
index 06e097a36..8ca529aa3 100644
--- a/internal/git/objectpool/fetch_test.go
+++ b/internal/git/objectpool/fetch_test.go
@@ -24,7 +24,10 @@ import (
 
 func TestFetchFromOrigin_dangling(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchFromOriginDangling)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchFromOriginDangling)
 }
 
 func testFetchFromOriginDangling(t *testing.T, ctx context.Context) {
@@ -113,7 +116,10 @@ func TestFetchFromOrigin_fsck(t *testing.T) {
 
 func TestFetchFromOrigin_deltaIslands(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchFromOriginDeltaIslands)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchFromOriginDeltaIslands)
 }
 
 func testFetchFromOriginDeltaIslands(t *testing.T, ctx context.Context) {
@@ -126,6 +132,13 @@ func testFetchFromOriginDeltaIslands(t *testing.T, ctx context.Context) {
 	require.NoError(t, pool.FetchFromOrigin(ctx, repo), "seed pool")
 	require.NoError(t, pool.Link(ctx, repo))
 
+	// With multi-pack-indices we don't do full repacks of repositories that
+	// aggressively anymore, but in order to test delta islands we need to trigger one.
+	// We thus write a second packfile so that `OptimizeRepository()` decides to
+	// rewrite packfiles.
+	gittest.WriteCommit(t, cfg, poolPath, gittest.WithBranch("irrelevant"))
+	gittest.Exec(t, cfg, "-C", poolPath, "repack")
+
 	// The setup of delta islands is done in the normal repository, and thus we pass `false`
 	// for `isPoolRepo`. Verification whether we correctly handle repacking though happens in
 	// the pool repository.
@@ -136,7 +149,10 @@ func testFetchFromOriginDeltaIslands(t *testing.T, ctx context.Context) {
 
 func TestFetchFromOrigin_bitmapHashCache(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchFromOriginBitmapHashCache)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchFromOriginBitmapHashCache)
 }
 
 func testFetchFromOriginBitmapHashCache(t *testing.T, ctx context.Context) {
@@ -166,7 +182,10 @@ func testFetchFromOriginBitmapHashCache(t *testing.T, ctx context.Context) {
 
 func TestFetchFromOrigin_refUpdates(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchFromOriginRefUpdates)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchFromOriginRefUpdates)
 }
 
 func testFetchFromOriginRefUpdates(t *testing.T, ctx context.Context) {
@@ -217,7 +236,10 @@ func testFetchFromOriginRefUpdates(t *testing.T, ctx context.Context) {
 
 func TestFetchFromOrigin_refs(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchFromOriginRefs)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchFromOriginRefs)
 }
 
 func testFetchFromOriginRefs(t *testing.T, ctx context.Context) {
diff --git a/internal/gitaly/service/objectpool/fetch_into_object_pool_test.go b/internal/gitaly/service/objectpool/fetch_into_object_pool_test.go
index a50f49e00..2d9bec21c 100644
--- a/internal/gitaly/service/objectpool/fetch_into_object_pool_test.go
+++ b/internal/gitaly/service/objectpool/fetch_into_object_pool_test.go
@@ -38,7 +38,10 @@ import (
 
 func TestFetchIntoObjectPool_Success(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchIntoObjectPoolSuccess)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchIntoObjectPoolSuccess)
 }
 
 func testFetchIntoObjectPoolSuccess(t *testing.T, ctx context.Context) {
@@ -91,7 +94,10 @@ func testFetchIntoObjectPoolSuccess(t *testing.T, ctx context.Context) {
 
 func TestFetchIntoObjectPool_transactional(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchIntoObjectPoolTransactional)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchIntoObjectPoolTransactional)
 }
 
 func testFetchIntoObjectPoolTransactional(t *testing.T, ctx context.Context) {
@@ -207,7 +213,10 @@ func testFetchIntoObjectPoolTransactional(t *testing.T, ctx context.Context) {
 
 func TestFetchIntoObjectPool_CollectLogStatistics(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchIntoObjectPoolCollectLogStatistics)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchIntoObjectPoolCollectLogStatistics)
 }
 
 func testFetchIntoObjectPoolCollectLogStatistics(t *testing.T, ctx context.Context) {
@@ -303,7 +312,10 @@ func TestFetchIntoObjectPool_Failure(t *testing.T) {
 
 func TestFetchIntoObjectPool_dfConflict(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testFetchIntoObjectPoolDfConflict)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testFetchIntoObjectPoolDfConflict)
 }
 
 func testFetchIntoObjectPoolDfConflict(t *testing.T, ctx context.Context) {
diff --git a/internal/gitaly/service/repository/optimize_test.go b/internal/gitaly/service/repository/optimize_test.go
index f713de3c2..618a6f2b5 100644
--- a/internal/gitaly/service/repository/optimize_test.go
+++ b/internal/gitaly/service/repository/optimize_test.go
@@ -28,7 +28,10 @@ import (
 
 func TestOptimizeRepository(t *testing.T) {
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.WriteBitmapLookupTable).Run(t, testOptimizeRepository)
+	testhelper.NewFeatureSets(
+		featureflag.WriteBitmapLookupTable,
+		featureflag.WriteMultiPackIndex,
+	).Run(t, testOptimizeRepository)
 }
 
 func testOptimizeRepository(t *testing.T, ctx context.Context) {
diff --git a/internal/metadata/featureflag/ff_write_multi_pack_index.go b/internal/metadata/featureflag/ff_write_multi_pack_index.go
new file mode 100644
index 000000000..9f2565788
--- /dev/null
+++ b/internal/metadata/featureflag/ff_write_multi_pack_index.go
@@ -0,0 +1,10 @@
+package featureflag
+
+// WriteMultiPackIndex determines whether Gitaly should write multi-pack-indices in
+// OptimizeRepository.
+var WriteMultiPackIndex = NewFeatureFlag(
+	"write_multi_pack_index",
+	"v15.9.0",
+	"https://gitlab.com/gitlab-org/gitaly/-/issues/4741",
+	false,
+)