diff --git a/cmd/zoekt-merge-index/main.go b/cmd/zoekt-merge-index/main.go
index 4dee521f1..899d52b93 100644
--- a/cmd/zoekt-merge-index/main.go
+++ b/cmd/zoekt-merge-index/main.go
@@ -11,18 +11,20 @@ import (
 	"github.com/sourcegraph/zoekt"
 )
 
-func merge(dstDir string, names []string) error {
+// merge merges the input shards into a compound shard in dstDir. It returns the
+// full path to the compound shard. The input shards are removed on success.
+func merge(dstDir string, names []string) (string, error) {
 	var files []zoekt.IndexFile
 	for _, fn := range names {
 		f, err := os.Open(fn)
 		if err != nil {
-			return err
+			return "", nil
 		}
 		defer f.Close()
 
 		indexFile, err := zoekt.NewIndexFile(f)
 		if err != nil {
-			return err
+			return "", err
 		}
 		defer indexFile.Close()
 
@@ -31,18 +33,18 @@ func merge(dstDir string, names []string) error {
 
 	tmpName, dstName, err := zoekt.Merge(dstDir, files...)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	// Delete input shards.
 	for _, name := range names {
 		paths, err := zoekt.IndexFilePaths(name)
 		if err != nil {
-			return fmt.Errorf("zoekt-merge-index: %w", err)
+			return "", fmt.Errorf("zoekt-merge-index: %w", err)
 		}
 		for _, p := range paths {
 			if err := os.Remove(p); err != nil {
-				return fmt.Errorf("zoekt-merge-index: failed to remove simple shard: %w", err)
+				return "", fmt.Errorf("zoekt-merge-index: failed to remove simple shard: %w", err)
 			}
 		}
 	}
@@ -50,12 +52,13 @@ func merge(dstDir string, names []string) error {
 	// We only rename the compound shard if all simple shards could be deleted in the
 	// previous step. This guarantees we won't have duplicate indexes.
 	if err := os.Rename(tmpName, dstName); err != nil {
-		return fmt.Errorf("zoekt-merge-index: failed to rename compound shard: %w", err)
+		return "", fmt.Errorf("zoekt-merge-index: failed to rename compound shard: %w", err)
 	}
-	return nil
+
+	return dstName, nil
 }
 
-func mergeCmd(paths []string) error {
+func mergeCmd(paths []string) (string, error) {
 	if paths[0] == "-" {
 		paths = []string{}
 		scanner := bufio.NewScanner(os.Stdin)
@@ -63,7 +66,7 @@ func mergeCmd(paths []string) error {
 			paths = append(paths, strings.TrimSpace(scanner.Text()))
 		}
 		if err := scanner.Err(); err != nil {
-			return err
+			return "", err
 		}
 		log.Printf("merging %d paths from stdin", len(paths))
 	}
@@ -129,9 +132,11 @@ func explodeCmd(path string) error {
 func main() {
 	switch subCommand := os.Args[1]; subCommand {
 	case "merge":
-		if err := mergeCmd(os.Args[2:]); err != nil {
+		compoundShardPath, err := mergeCmd(os.Args[2:])
+		if err != nil {
 			log.Fatal(err)
 		}
+		fmt.Println(compoundShardPath)
 	case "explode":
 		if err := explodeCmd(os.Args[2]); err != nil {
 			log.Fatal(err)
diff --git a/cmd/zoekt-merge-index/main_test.go b/cmd/zoekt-merge-index/main_test.go
index 48058eb0f..5622cb295 100644
--- a/cmd/zoekt-merge-index/main_test.go
+++ b/cmd/zoekt-merge-index/main_test.go
@@ -8,6 +8,8 @@ import (
 	"sort"
 	"testing"
 
+	"github.com/stretchr/testify/require"
+
 	"github.com/sourcegraph/zoekt"
 	"github.com/sourcegraph/zoekt/query"
 	"github.com/sourcegraph/zoekt/shards"
@@ -15,97 +17,71 @@ import (
 
 func TestMerge(t *testing.T) {
 	v16Shards, err := filepath.Glob("../../testdata/shards/*_v16.*.zoekt")
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	sort.Strings(v16Shards)
 
 	testShards, err := copyTestShards(t.TempDir(), v16Shards)
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	t.Log(testShards)
 
 	dir := t.TempDir()
-	err = merge(dir, testShards)
-	if err != nil {
-		t.Fatal(err)
-	}
+	cs, err := merge(dir, testShards)
+	require.NoError(t, err)
+	// The name of the compound shard is based on the merged repos, so it should be
+	// stable
+	require.Equal(t, filepath.Base(cs), "compound-ea9613e2ffba7d7361856aebfca75fb714856509_v17.00000.zoekt")
 
 	ss, err := shards.NewDirectorySearcher(dir)
-	if err != nil {
-		t.Fatalf("NewDirectorySearcher(%s): %v", dir, err)
-	}
+	require.NoError(t, err)
 	defer ss.Close()
 
 	q, err := query.Parse("hello")
-	if err != nil {
-		t.Fatalf("Parse(hello): %v", err)
-	}
+	require.NoError(t, err)
 
 	var sOpts zoekt.SearchOptions
 	ctx := context.Background()
 	result, err := ss.Search(ctx, q, &sOpts)
-	if err != nil {
-		t.Fatalf("Search(%v): %v", q, err)
-	}
+	require.NoError(t, err)
 
 	// we are merging the same shard twice, so we expect the same file twice.
-	if len(result.Files) != 2 {
-		t.Errorf("got %v, want 2 files.", result.Files)
-	}
+	require.Len(t, result.Files, 2)
 }
 
 // Merge 2 simple shards and then explode them.
 func TestExplode(t *testing.T) {
 	v16Shards, err := filepath.Glob("../../testdata/shards/repo*_v16.*.zoekt")
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	sort.Strings(v16Shards)
 
 	testShards, err := copyTestShards(t.TempDir(), v16Shards)
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	t.Log(testShards)
 
 	dir := t.TempDir()
-	err = merge(dir, testShards)
-	if err != nil {
-		t.Fatal(err)
-	}
+	_, err = merge(dir, testShards)
+	require.NoError(t, err)
 
 	cs, err := filepath.Glob(filepath.Join(dir, "compound-*.zoekt"))
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	err = explode(dir, cs[0])
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 
 	cs, err = filepath.Glob(filepath.Join(dir, "compound-*.zoekt"))
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
+
 	if len(cs) != 0 {
 		t.Fatalf("explode should have deleted the compound shard if it returned without error")
 	}
 
 	exploded, err := filepath.Glob(filepath.Join(dir, "*.zoekt"))
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 
 	if len(exploded) != len(testShards) {
 		t.Fatalf("the number of simple shards before %d and after %d should be the same", len(testShards), len(exploded))
 	}
 
 	ss, err := shards.NewDirectorySearcher(dir)
-	if err != nil {
-		t.Fatalf("NewDirectorySearcher(%s): %v", dir, err)
-	}
+	require.NoError(t, err)
 	defer ss.Close()
 
 	var sOpts zoekt.SearchOptions
@@ -132,16 +108,10 @@ func TestExplode(t *testing.T) {
 	for _, c := range cases {
 		t.Run(c.searchLiteral, func(t *testing.T) {
 			q, err := query.Parse(c.searchLiteral)
-			if err != nil {
-				t.Fatalf("Parse(%s): %v", c.searchLiteral, err)
-			}
+			require.NoError(t, err)
 			result, err := ss.Search(ctx, q, &sOpts)
-			if err != nil {
-				t.Fatalf("Search(%v): %v", q, err)
-			}
-			if got := len(result.Files); got != c.wantResults {
-				t.Fatalf("wanted %d results, got %d", c.wantResults, got)
-			}
+			require.NoError(t, err)
+			require.Len(t, result.Files, c.wantResults)
 		})
 	}
 }
diff --git a/cmd/zoekt-sourcegraph-indexserver/cleanup.go b/cmd/zoekt-sourcegraph-indexserver/cleanup.go
index 79b3fe74c..e8282e731 100644
--- a/cmd/zoekt-sourcegraph-indexserver/cleanup.go
+++ b/cmd/zoekt-sourcegraph-indexserver/cleanup.go
@@ -422,8 +422,9 @@ func (s *Server) vacuum() {
 			})
 
 			if err != nil {
-				log.Printf("failed to explode compound shard %s: %s", path, string(b))
+				log.Printf("failed to explode compound shard: shard=%s out=%s err=%s", path, string(b), err)
 			}
+			log.Printf("exploded compound shard: shard=%s", path)
 			continue
 		}
 
@@ -432,7 +433,7 @@ func (s *Server) vacuum() {
 		})
 
 		if err != nil {
-			log.Printf("error while removing tombstones in %s: %s", fn, err)
+			log.Printf("error while removing tombstones in %s: %s", path, err)
 		}
 	}
 }
diff --git a/cmd/zoekt-sourcegraph-indexserver/merge.go b/cmd/zoekt-sourcegraph-indexserver/merge.go
index 9d3cf8533..904a33748 100644
--- a/cmd/zoekt-sourcegraph-indexserver/merge.go
+++ b/cmd/zoekt-sourcegraph-indexserver/merge.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"log"
 	"os"
 	"os/exec"
@@ -88,14 +89,25 @@ func (s *Server) merge(mergeCmd func(args ...string) *exec.Cmd) {
 			}
 
 			start := time.Now()
-			out, err := mergeCmd(paths...).CombinedOutput()
+
+			cmd := mergeCmd(paths...)
+
+			// zoekt-merge-index writes the full path of the new compound shard to stdout.
+			stdoutBuf := &bytes.Buffer{}
+			stderrBuf := &bytes.Buffer{}
+			cmd.Stdout = stdoutBuf
+			cmd.Stderr = stderrBuf
+
+			err := cmd.Run()
 
 			metricShardMergingDuration.WithLabelValues(strconv.FormatBool(err != nil)).Observe(time.Since(start).Seconds())
 			if err != nil {
-				log.Printf("mergeCmd: out=%s, err=%s", out, err)
+				log.Printf("error merging shards: stdout=%s, stderr=%s, err=%s", stdoutBuf.String(), stderrBuf.String(), err)
 				return
 			}
 
+			log.Printf("finished merging: shard=%s durationSeconds=%.2f", stdoutBuf.String(), time.Since(start).Seconds())
+
 			next = true
 		})
 	}