indexserver: add debug endpoint for deleting repository shards

cmd/zoekt-sourcegraph-indexserver/debug.go

@@ -95,6 +95,10 @@ func debugCmd() *ffcli.Command {
     "wget -q -O - http://localhost:6072/metrics -sS | grep index_shard_merging_running". It is only possible
     to trigger one merge operation at a time.
 
+  wget -q -O - http://localhost:6072/debug/delete?id=[REPOSITORY_ID]
+	delete all of the shards associated with the given repository id. You can find the id associated with a 
+	repository via the "/debug/indexed" route.
+
   wget -q -O - http://localhost:6072/debug/queue
     list the repositories in the indexing queue, sorted by descending priority.
 

cmd/zoekt-sourcegraph-indexserver/main.go

@@ -646,6 +646,7 @@ func (s *Server) addDebugHandlers(mux *http.ServeMux) {
 	// on "/".
 	mux.Handle("/", http.HandlerFunc(s.handleReIndex))
 
+	mux.Handle("/debug/delete", http.HandlerFunc(s.handleDebugDelete))
 	mux.Handle("/debug/indexed", http.HandlerFunc(s.handleDebugIndexed))
 	mux.Handle("/debug/list", http.HandlerFunc(s.handleDebugList))
 	mux.Handle("/debug/merge", http.HandlerFunc(s.handleDebugMerge))
@@ -757,6 +758,105 @@ func (s *Server) handleDebugList(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (s *Server) handleDebugDelete(w http.ResponseWriter, r *http.Request) {
+	rawID := r.URL.Query().Get("id")
+	if rawID == "" {
+		http.Error(w, "URL parameter 'id' must be specified", http.StatusBadRequest)
+		return
+	}
+
+	id64, err := strconv.ParseUint(rawID, 10, 32)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to parse repository id %q as uint32: %s", rawID, err), http.StatusBadRequest)
+		return
+	}
+
+	repoID := uint32(id64)
+
+	s.queue.mu.Lock()
+	defer s.queue.mu.Unlock()
+
+	item := s.queue.get(repoID)
+	if item == nil {
+		http.Error(w, fmt.Sprintf("no repository found for id %q", rawID), http.StatusBadRequest)
+		return
+	}
+
+	var deletionError error
+
+	repoName := item.opts.Name
+	s.muIndexDir.With(repoName, func() {
+		o := s.indexArgs(item.opts).BuildOptions()
+		deletionError = deleteShards(o)
+	})
+
+	if deletionError != nil {
+		http.Error(w, fmt.Sprintf("while deleting shards for repository id %q: %s", rawID, deletionError), http.StatusInternalServerError)
+		return
+	}
+}
+
+// deleteShards deletes all the shards that are associated with the repository specified
+// in the build options.
+//
+// Users must hold the indexDir lock for this repository before calling deleteShards.
+func deleteShards(options *build.Options) error {
+	shardPaths := options.FindAllShards()
+
+	// Ensure that the paths are in reverse sorted order to ensure that Zoekt's repository <-> shard matching logic
+	// works correctly.
+	//
+	// Example: - repoA_v16.00002.zoekt
+	//          - repoA_v16.00001.zoekt
+	//          - repoA_v16.00000.zoekt
+	//
+	// zoekt-indexserver checks whether it has indexed "repoA" by first checking to see if the 0th shard
+	// is present (repoA_v16.00000.zoekt). If it's present, then it gathers all rest of the shards names in ascending order
+	// (...00001.zoekt, ...00002.zoekt). If it's missing, then zoekt assumes that it never indexed "repoA".
+	//
+	// If this function were to crash while deleting repoA and we only deleted the 0th shard, then shard's 1 & 2 would never
+	// be cleaned up by Zoekt indexserver (since the 0th shard is the only shard that's tested).
+	//
+	// Ensuring that we delete shards in reverse sorted order (2 -> 1 -> 0) always ensures that we don't leave an inconsistent
+	// state behind even if we crash.
+
+	sort.Slice(shardPaths, func(i, j int) bool {
+		return shardPaths[i] > shardPaths[j]
+	})
+
+	for _, shard := range shardPaths {
+		// Is this repository inside a compound shard? If so, set a tombstone
+		// instead of deleting the shard outright.
+		if zoekt.ShardMergingEnabled() && strings.HasPrefix(filepath.Base(shard), "compound-") {
+			if !strings.HasSuffix(shard, ".zoekt") {
+				continue
+			}
+
+			err := zoekt.SetTombstone(shard, options.RepositoryDescription.ID)
+			if err != nil {
+				return fmt.Errorf("setting tombstone in shard %q: %w", shard, err)
+			}
+
+			continue
+		}
+
+		metaFile := shard + ".meta"
+		if _, err := os.Stat(metaFile); err == nil {
+			err := os.Remove(metaFile)
+			if err != nil {
+				return fmt.Errorf("deleting metadata file %q: %w", metaFile, err)
+			}
+		}
+
+		err := os.Remove(shard)
+		if err != nil {
+			return fmt.Errorf("deleting shard %q: %w", shard, err)
+		}
+	}
+
+	return nil
+}
+
 // handleDebugMerge triggers a merge even if shard merging is not enabled. Users
 // can run this command during periods of low usage (evenings, weekends) to
 // trigger an initial merge run. In the steady-state, merges happen rarely, even