diff --git a/proxy/proxy.go b/proxy/proxy.go
index f29878e..5c905f0 100644
--- a/proxy/proxy.go
+++ b/proxy/proxy.go
@@ -72,7 +72,7 @@ type SNIProxy struct {
 }
 
 type activeTunnel struct {
-	conns []net.Conn
+	conns map[net.Conn]struct{}
 }
 
 // readOnlyConn is a wrapper for io.Reader that implements net.Conn
@@ -592,26 +592,19 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 	p.activeTunnelsLock.Lock()
 	tunnel, ok := p.activeTunnels[hostname]
 	if !ok {
-		tunnel = &activeTunnel{}
+		tunnel = &activeTunnel{conns: make(map[net.Conn]struct{})}
 		p.activeTunnels[hostname] = tunnel
 	}
-	tunnel.conns = append(tunnel.conns, actualClientConn)
+	tunnel.conns[actualClientConn] = struct{}{}
 	p.activeTunnelsLock.Unlock()
 
 	defer func() {
-		// Remove this conn from active tunnels
+		// Remove this conn from active tunnels - O(1) with map
 		p.activeTunnelsLock.Lock()
 		if tunnel, ok := p.activeTunnels[hostname]; ok {
-			newConns := make([]net.Conn, 0, len(tunnel.conns))
-			for _, c := range tunnel.conns {
-				if c != actualClientConn {
-					newConns = append(newConns, c)
-				}
-			}
-			if len(newConns) == 0 {
+			delete(tunnel.conns, actualClientConn)
+			if len(tunnel.conns) == 0 {
 				delete(p.activeTunnels, hostname)
-			} else {
-				tunnel.conns = newConns
 			}
 		}
 		p.activeTunnelsLock.Unlock()
@@ -810,32 +803,42 @@ func (p *SNIProxy) ClearCache() {
 
 // UpdateLocalSNIs updates the local SNIs and invalidates cache for changed domains
 func (p *SNIProxy) UpdateLocalSNIs(fullDomains []string) {
-	newSNIs := make(map[string]struct{})
+	newSNIs := make(map[string]struct{}, len(fullDomains))
 	for _, domain := range fullDomains {
 		newSNIs[domain] = struct{}{}
-		// Invalidate any cached route for this domain
-		p.cache.Delete(domain)
 	}
 
-	// Update localSNIs
-	p.localSNIsLock.Lock()
+	// Get old SNIs with read lock to compute diff outside write lock
+	p.localSNIsLock.RLock()
+	oldSNIs := p.localSNIs
+	p.localSNIsLock.RUnlock()
+
+	// Compute removed SNIs outside the lock
 	removed := make([]string, 0)
-	for sni := range p.localSNIs {
+	for sni := range oldSNIs {
 		if _, stillLocal := newSNIs[sni]; !stillLocal {
 			removed = append(removed, sni)
 		}
 	}
+
+	// Swap with minimal write lock hold time
+	p.localSNIsLock.Lock()
 	p.localSNIs = newSNIs
 	p.localSNIsLock.Unlock()
 
+	// Invalidate cache for new domains (cache is thread-safe)
+	for domain := range newSNIs {
+		p.cache.Delete(domain)
+	}
+
 	logger.Debug("Updated local SNIs, added %d, removed %d", len(newSNIs), len(removed))
 
 	// Terminate tunnels for removed SNIs
 	if len(removed) > 0 {
 		p.activeTunnelsLock.Lock()
 		for _, sni := range removed {
-			if tunnels, ok := p.activeTunnels[sni]; ok {
-				for _, conn := range tunnels.conns {
+			if tunnel, ok := p.activeTunnels[sni]; ok {
+				for conn := range tunnel.conns {
 					conn.Close()
 				}
 				delete(p.activeTunnels, sni)