diff --git a/lib/index/mu-indexer.cc b/lib/index/mu-indexer.cc
index d373040c..72a12a0a 100644
--- a/lib/index/mu-indexer.cc
+++ b/lib/index/mu-indexer.cc
@@ -22,6 +22,7 @@
 #include <config.h>
 
 #include <atomic>
+#include <algorithm>
 #include <mutex>
 #include <vector>
 #include <thread>
@@ -39,29 +40,41 @@ using namespace std::chrono_literals;
 using namespace Mu;
 
 struct IndexState {
-	enum State { Idle, Scanning, Cleaning };
+	enum State { Idle,
+		     Scanning,
+		     Cleaning };
 	static const char* name(State s)
 	{
 		switch (s) {
-		case Idle: return "idle";
-		case Scanning: return "scanning";
-		case Cleaning: return "cleaning";
-		default: return "<error>";
+		case Idle:
+			return "idle";
+		case Scanning:
+			return "scanning";
+		case Cleaning:
+			return "cleaning";
+		default:
+			return "<error>";
 		}
 	}
 
-	bool operator==(State rhs) const { return state_ == rhs; }
+	bool operator==(State rhs) const
+	{
+		return state_ == rhs;
+	}
+	bool operator!=(State rhs) const
+	{
+		return state_ != rhs;
+	}
 
 	void change_to(State new_state)
 	{
-		g_debug("changing indexer state %s->%s",
-		        name((State)state_),
+		g_debug("changing indexer state %s->%s", name((State)state_),
 		        name((State)new_state));
 		state_ = new_state;
 	}
 
 private:
-	State state_{Idle};
+	std::atomic<State> state_{Idle};
 };
 
 struct Indexer::Private {
@@ -74,17 +87,20 @@ struct Indexer::Private {
 	{
 		g_message("created indexer for %s -> %s (batch-size: %zu)",
 		          store.metadata().root_maildir.c_str(),
-		          store.metadata().database_path.c_str(),
-		          store.metadata().batch_size);
+		          store.metadata().database_path.c_str(), store.metadata().batch_size);
 	}
 
-	~Private() { stop(); }
+	~Private()
+	{
+		stop();
+	}
 
 	bool dir_predicate(const std::string& path, const struct dirent* dirent) const;
 	bool handler(const std::string& fullpath, struct stat* statbuf, Scanner::HandleType htype);
 
 	void maybe_start_worker();
-	void worker();
+	void item_worker();
+	void scan_worker();
 
 	bool cleanup();
 
@@ -101,17 +117,24 @@ struct Indexer::Private {
 	std::vector<std::thread> workers_;
 	std::thread              scanner_worker_;
 
-	AsyncQueue<std::string> fq_;
+	struct WorkItem {
+		std::string full_path;
+		enum Type {
+			Dir,
+			File
+		};
+		Type type;
+	};
+
+	AsyncQueue<WorkItem> todos_;
 
 	Progress   progress_;
 	IndexState state_;
-
-	std::mutex lock_, wlock_;
+	std::mutex lock_, w_lock_;
 };
 
 bool
-Indexer::Private::handler(const std::string&  fullpath,
-                          struct stat*        statbuf,
+Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
                           Scanner::HandleType htype)
 {
 	switch (htype) {
@@ -124,8 +147,7 @@ Indexer::Private::handler(const std::string&  fullpath,
 		dirstamp_ = store_.dirstamp(fullpath);
 		if (conf_.lazy_check && dirstamp_ >= statbuf->st_mtime &&
 		    htype == Scanner::HandleType::EnterNewCur) {
-			g_debug("skip %s (seems up-to-date: %s >= %s)",
-			        fullpath.c_str(),
+			g_debug("skip %s (seems up-to-date: %s >= %s)", fullpath.c_str(),
 			        time_to_string("%FT%T", dirstamp_).c_str(),
 			        time_to_string("%FT%T", statbuf->st_mtime).c_str());
 			return false;
@@ -152,7 +174,7 @@ Indexer::Private::handler(const std::string&  fullpath,
 		return true;
 	}
 	case Scanner::HandleType::LeaveDir: {
-		store_.set_dirstamp(fullpath, ::time(NULL));
+		todos_.push({fullpath, WorkItem::Type::Dir});
 		return true;
 	}
 
@@ -160,8 +182,7 @@ Indexer::Private::handler(const std::string&  fullpath,
 		++progress_.checked;
 
 		if ((size_t)statbuf->st_size > max_message_size_) {
-			g_debug("skip %s (too big: %" G_GINT64_FORMAT " bytes)",
-			        fullpath.c_str(),
+			g_debug("skip %s (too big: %" G_GINT64_FORMAT " bytes)", fullpath.c_str(),
 			        (gint64)statbuf->st_size);
 			return false;
 		}
@@ -175,44 +196,59 @@ Indexer::Private::handler(const std::string&  fullpath,
 
 		// push the remaining messages to our "todo" queue for
 		// (re)parsing and adding/updating to the database.
-		fq_.push(std::string{fullpath});
+		todos_.push({fullpath, WorkItem::Type::File});
 		return true;
 	}
-	default: g_return_val_if_reached(false); return false;
+	default:
+		g_return_val_if_reached(false);
+		return false;
 	}
 }
 
 void
 Indexer::Private::maybe_start_worker()
 {
-	std::lock_guard<std::mutex> wlock{wlock_};
+	std::lock_guard lock{w_lock_};
 
-	if (fq_.size() > workers_.size() && workers_.size() < max_workers_)
-		workers_.emplace_back(std::thread([this] { worker(); }));
+	if (todos_.size() > workers_.size() && workers_.size() < max_workers_) {
+		workers_.emplace_back(std::thread([this] { item_worker(); }));
+		g_debug("added worker %zu", workers_.size());
+	}
 }
 
 void
-Indexer::Private::worker()
+Indexer::Private::item_worker()
 {
-	std::string item;
+	WorkItem item;
 
 	g_debug("started worker");
 
 	while (state_ == IndexState::Scanning) {
-
-		if (!fq_.pop(item, 250ms))
+		if (!todos_.pop(item, 250ms))
 			continue;
 		try {
-			std::unique_lock lock{lock_};
-
- 			store_.add_message(item, true /*use-transaction*/);
-			++progress_.updated;
-
+			std::lock_guard lock{w_lock_};
+			switch (item.type) {
+			case WorkItem::Type::File:
+				store_.add_message(item.full_path,
+				                   true /*use-transaction*/);
+				++progress_.updated;
+				break;
+			case WorkItem::Type::Dir:
+				store_.set_dirstamp(item.full_path, ::time(NULL),
+				                    true /*use-transaction*/);
+				break;
+			default:
+				g_warn_if_reached();
+				break;
+			}
 		} catch (const Mu::Error& er) {
-			g_warning("error adding message @ %s: %s", item.c_str(), er.what());
+			g_warning("error adding message @ %s: %s",
+			          item.full_path.c_str(), er.what());
 		}
 
 		maybe_start_worker();
+		std::this_thread::yield();
 	}
 }
 
@@ -227,8 +263,7 @@ Indexer::Private::cleanup()
 		++n;
 		if (::access(path.c_str(), R_OK) != 0) {
 			g_debug("cannot read %s (id=%u); queueing for removal from store",
-			        path.c_str(),
-			        id);
+			        path.c_str(), id);
 			orphans.emplace_back(id);
 		}
 
@@ -246,59 +281,67 @@ Indexer::Private::cleanup()
 	return true;
 }
 
+void
+Indexer::Private::scan_worker()
+{
+	progress_ = {};
+
+	if (conf_.scan) {
+		g_debug("starting scanner");
+		if (!scanner_.start()) { // blocks.
+			g_warning("failed to start scanner");
+			goto leave;
+		}
+		g_debug("scanner finished with %zu file(s) in queue", todos_.size());
+	}
+
+	// now there may still be messages in the work queue...
+	// finish those; this is a bit ugly; perhaps we should
+	// handle SIGTERM etc.
+	if (!todos_.empty())
+		g_debug("process %zu remaining message(s) with %zu worker(s)", todos_.size(),
+		        workers_.size());
+	while (!todos_.empty())
+		std::this_thread::sleep_for(100ms);
+
+	store_.commit();
+
+	if (conf_.cleanup) {
+		g_debug("starting cleanup");
+		state_.change_to(IndexState::Cleaning);
+		cleanup();
+		g_debug("cleanup finished");
+	}
+leave:
+	state_.change_to(IndexState::Idle);
+}
+
 bool
 Indexer::Private::start(const Indexer::Config& conf)
 {
 	stop();
 
 	conf_ = conf;
-	if (conf_.max_threads == 0)
-		max_workers_ = std::thread::hardware_concurrency();
-	else
+	if (conf_.max_threads == 0) {
+		/* we're blocked mostly by a) filesystem and b) database;
+		 * so it's not very useful to start many threads */
+		max_workers_ = std::max(
+		    4U, std::thread::hardware_concurrency());
+	} else
 		max_workers_ = conf.max_threads;
 
 	g_debug("starting indexer with <= %zu worker thread(s)", max_workers_);
-	g_debug("indexing: %s; clean-up: %s",
-	        conf_.scan ? "yes" : "no",
+	g_debug("indexing: %s; clean-up: %s", conf_.scan ? "yes" : "no",
 	        conf_.cleanup ? "yes" : "no");
 
 	state_.change_to(IndexState::Scanning);
-	{
-		/* kick off the first worker, which will spawn more if needed. */
-		std::lock_guard<std::mutex> wlock{wlock_};
-		workers_.emplace_back(std::thread([this] { worker(); }));
-	}
-	scanner_worker_ = std::thread([this] {
-		progress_ = {};
-
-		if (conf_.scan) {
-			g_debug("starting scanner");
-			if (!scanner_.start()) { // blocks.
-				g_warning("failed to start scanner");
-				goto leave;
-			}
-			g_debug("scanner finished with %zu file(s) in queue", fq_.size());
-		}
-
-		// now there may still be messages in the work queue...
-		// finish those; this is a bit ugly; perhaps we should
-		// handle SIGTERM etc.
-		while (!fq_.empty())
-			std::this_thread::sleep_for(100ms);
-
-		store_.commit();
-
-		if (conf_.cleanup) {
-			g_debug("starting cleanup");
-			state_.change_to(IndexState::Cleaning);
-			cleanup();
-			g_debug("cleanup finished");
-		}
-	leave:
-		state_.change_to(IndexState::Idle);
-	});
+	/* kick off the first worker, which will spawn more if needed. */
+	workers_.emplace_back(std::thread([this] { item_worker(); }));
+	/* kick the disk-scanner thread */
+	scanner_worker_ = std::thread([this] { scan_worker(); });
 
 	g_debug("started indexer");
+
 	return true;
 }
 
@@ -306,26 +349,24 @@ bool
 Indexer::Private::stop()
 {
 	scanner_.stop();
-	state_.change_to(IndexState::Idle);
 
-	const auto w_n = workers_.size();
-
-	fq_.clear();
+	todos_.clear();
 	if (scanner_worker_.joinable())
 		scanner_worker_.join();
 
+	state_.change_to(IndexState::Idle);
 	for (auto&& w : workers_)
 		if (w.joinable())
 			w.join();
 	workers_.clear();
 
-	if (w_n > 0)
-		g_debug("stopped indexer (joined %zu worker(s))", w_n);
-
 	return true;
 }
 
-Indexer::Indexer(Store& store) : priv_{std::make_unique<Private>(store)} {}
+Indexer::Indexer(Store& store)
+    : priv_{std::make_unique<Private>(store)}
+{
+}
 
 Indexer::~Indexer() = default;
 
@@ -338,7 +379,7 @@ Indexer::start(const Indexer::Config& conf)
 		return false;
 	}
 
-	std::lock_guard<std::mutex> l(priv_->lock_);
+	std::lock_guard lock(priv_->lock_);
 	if (is_running())
 		return true;
 
@@ -348,7 +389,7 @@ Indexer::start(const Indexer::Config& conf)
 bool
 Indexer::stop()
 {
-	std::lock_guard<std::mutex> l(priv_->lock_);
+	std::lock_guard lock{priv_->lock_};
 
 	if (!is_running())
 		return true;
@@ -360,7 +401,7 @@ Indexer::stop()
 bool
 Indexer::is_running() const
 {
-	return !(priv_->state_ == IndexState::Idle) || !priv_->fq_.empty();
+	return priv_->state_ != IndexState::Idle;
 }
 
 Indexer::Progress
diff --git a/lib/index/mu-indexer.hh b/lib/index/mu-indexer.hh
index 78527445..2df7f1c6 100644
--- a/lib/index/mu-indexer.hh
+++ b/lib/index/mu-indexer.hh
@@ -58,7 +58,9 @@ public:
 	};
 
 	/**
-	 * Start indexing. If already underway, do nothing.
+	 * Start indexing. If already underway, do nothing. This returns
+	 * immediately after starting, with the work being done in the
+	 * background.
 	 *
 	 * @param conf a configuration object
 	 *
diff --git a/lib/index/mu-scanner.cc b/lib/index/mu-scanner.cc
index fbc9317b..dfa6984d 100644
--- a/lib/index/mu-scanner.cc
+++ b/lib/index/mu-scanner.cc
@@ -44,7 +44,10 @@ struct Scanner::Private {
 		if (!handler_)
 			throw Mu::Error{Error::Code::Internal, "missing handler"};
 	}
-	~Private() { stop(); }
+	~Private()
+	{
+		stop();
+	}
 
 	bool start();
 	bool stop();
@@ -65,7 +68,8 @@ is_special_dir(const char* d_name)
 }
 
 bool
-Scanner::Private::process_dentry(const std::string& path, struct dirent* dentry, bool is_maildir)
+Scanner::Private::process_dentry(const std::string& path, struct dirent* dentry,
+                                 bool is_maildir)
 {
 	const auto d_name{dentry->d_name};
 
@@ -83,9 +87,9 @@ Scanner::Private::process_dentry(const std::string& path, struct dirent* dentry,
 	if (S_ISDIR(statbuf.st_mode)) {
 		const auto new_cur =
 		    std::strcmp(d_name, "cur") == 0 || std::strcmp(d_name, "new") == 0;
-		const auto htype = new_cur ? Scanner::HandleType::EnterNewCur
-		                           : Scanner::HandleType::EnterDir;
-		const auto res   = handler_(fullpath, &statbuf, htype);
+		const auto htype =
+		    new_cur ? Scanner::HandleType::EnterNewCur : Scanner::HandleType::EnterDir;
+		const auto res = handler_(fullpath, &statbuf, htype);
 		if (!res)
 			return true; // skip
 
@@ -97,12 +101,16 @@ Scanner::Private::process_dentry(const std::string& path, struct dirent* dentry,
 		return handler_(fullpath, &statbuf, Scanner::HandleType::File);
 
 	g_debug("skip %s (neither maildir-file nor directory)", fullpath.c_str());
+
 	return true;
 }
 
 bool
 Scanner::Private::process_dir(const std::string& path, bool is_maildir)
 {
+	if (!running_)
+		return true; /* we're done */
+
 	const auto dir = opendir(path.c_str());
 	if (G_UNLIKELY(!dir)) {
 		g_warning("failed to scan dir %s: %s", path.c_str(), g_strerror(errno));
@@ -171,8 +179,7 @@ Scanner::Private::start()
 	const auto start{std::chrono::steady_clock::now()};
 	process_dir(root_dir_, is_maildir);
 	const auto elapsed = std::chrono::steady_clock::now() - start;
-	g_debug("finished scan of %s in %" G_GINT64_FORMAT " ms",
-	        root_dir_.c_str(),
+	g_debug("finished scan of %s in %" G_GINT64_FORMAT " ms", root_dir_.c_str(),
 	        to_ms(elapsed));
 	running_ = false;
 
@@ -201,15 +208,10 @@ Scanner::~Scanner() = default;
 bool
 Scanner::start()
 {
-	{
-		std::lock_guard<std::mutex> l(priv_->lock_);
-		if (priv_->running_)
-			return true; // nothing to do
+	if (priv_->running_)
+		return true; // nothing to do
 
-		priv_->running_ = true;
-	}
-
-	const auto res  = priv_->start();
+	const auto res  = priv_->start(); /* blocks */
 	priv_->running_ = false;
 
 	return res;
@@ -218,7 +220,7 @@ Scanner::start()
 bool
 Scanner::stop()
 {
-	std::lock_guard<std::mutex> l(priv_->lock_);
+	std::lock_guard l(priv_->lock_);
 
 	return priv_->stop();
 }
diff --git a/lib/mu-store.cc b/lib/mu-store.cc
index bce18875..75542db4 100644
--- a/lib/mu-store.cc
+++ b/lib/mu-store.cc
@@ -31,6 +31,7 @@
 #include <iostream>
 #include <cstring>
 
+#include <vector>
 #include <xapian.h>
 
 #include "mu-store.hh"
@@ -206,9 +207,12 @@ struct Store::Private {
 					                           contacts_.serialize());
 				});
 			}
-			g_debug("committing transaction (n=%zu)", transaction_size_);
+			g_debug("committing transaction (n=%zu,%zu)",
+			        transaction_size_, metadatas_.size());
 			xapian_try([this] {
 				writable_db().commit_transaction();
+				for (auto&& mdata : metadatas_)
+					writable_db().set_metadata(mdata.first, mdata.second);
 				transaction_size_ = 0;
 			});
 		}
@@ -278,6 +282,10 @@ struct Store::Private {
 	Xapian::docid    add_or_update_msg(Xapian::docid docid, MuMsg* msg);
 	Xapian::Document new_doc_from_message(MuMsg* msg);
 
+	/* metadata to write as part of a transaction commit */
+	using StringPair = std::pair<std::string, std::string>;
+	std::vector<StringPair> metadatas_;
+
 	const bool                        read_only_{};
 	std::unique_ptr<Xapian::Database> db_;
 
@@ -501,7 +509,7 @@ Store::dirstamp(const std::string& path) const
 }
 
 void
-Store::set_dirstamp(const std::string& path, time_t tstamp)
+Store::set_dirstamp(const std::string& path, time_t tstamp, bool use_transaction)
 {
 	std::lock_guard guard{priv_->lock_};
 
@@ -510,9 +518,15 @@ Store::set_dirstamp(const std::string& path, time_t tstamp)
 	const auto len = static_cast<size_t>(
 	    g_snprintf(data.data(), data.size(), "%zx", tstamp));
 
-	xapian_try([&] {
-		priv_->writable_db().set_metadata(path, std::string{data.data(), len});
-	});
+	/* set_metadata is not otherwise part of a "transaction" but we want it
+	 * to be so, so a dirstamp _only_ gets updated when the messages in the
+	 * dir are commited */
+
+	Private::StringPair item{path, std::string{data.data(), len}};
+	if (use_transaction)
+		priv_->metadatas_.emplace_back(std::move(item));
+	else
+		xapian_try([&] { priv_->writable_db().set_metadata(item.first, item.second); });
 }
 
 MuMsg*
diff --git a/lib/mu-store.hh b/lib/mu-store.hh
index f79fe930..6d72c35d 100644
--- a/lib/mu-store.hh
+++ b/lib/mu-store.hh
@@ -303,8 +303,10 @@ public:
 	 *
 	 * @param path a filesystem path
 	 * @param tstamp the timestamp for that path
+	 * @param whether to do this as part of a transaction
 	 */
-	void set_dirstamp(const std::string& path, time_t tstamp);
+	void set_dirstamp(const std::string& path, time_t tstamp,
+	                  bool use_transaction = false);
 
 	/**
 	 * Get the number of documents in the document database