diff --git a/server/protocol.py b/server/protocol.py
index 6eda042..7a77b1e 100644
--- a/server/protocol.py
+++ b/server/protocol.py
@@ -108,9 +108,11 @@ class ServerManager(LoggedClass):
 
     def notify(self, height, touched):
         '''Notify sessions about height changes and touched addresses.'''
-        sessions = [session for session in self.sessions
-                    if isinstance(session, ElectrumX)]
-        ElectrumX.notify(sessions, height, touched)
+        cache = {}
+        for session in self.sessions:
+            if isinstance(session, ElectrumX):
+                # Use a tuple to distinguish from JSON
+                session.jobs.put_nowait((height, touched, cache))
 
     def stop(self):
         '''Close listening servers.'''
@@ -196,7 +198,7 @@ class Session(JSONRPC):
         self.coin = bp.coin
         self.kind = kind
         self.hash168s = set()
-        self.requests = asyncio.Queue()
+        self.jobs = asyncio.Queue()
         self.current_task = None
         self.client = 'unknown'
 
@@ -222,26 +224,23 @@ class Session(JSONRPC):
 
     def on_json_request(self, request):
         '''Queue the request for asynchronous handling.'''
-        self.requests.put_nowait(request)
+        self.jobs.put_nowait(request)
 
     async def serve_requests(self):
         '''Asynchronously run through the task queue.'''
         while True:
             await asyncio.sleep(0)
-            request = await self.requests.get()
+            job = await self.jobs.get()
             try:
-                start = time.time()
-                await self.handle_json_request(request)
-                secs = time.time() - start
-                if secs > 1:
-                    self.logger.warning('slow request for {} took {:.1f}s: {}'
-                                        .format(self.peername(), secs,
-                                                request))
+                if isinstance(job, tuple):  # Height / mempool notification
+                    await self.notify(*job)
+                else:
+                    await self.handle_json_request(job)
             except asyncio.CancelledError:
                 break
             except Exception:
                 # Getting here should probably be considered a bug and fixed
-                self.logger.error('error handling request {}'.format(request))
+                self.logger.error('error handling request {}'.format(job))
                 traceback.print_exc()
 
     def peername(self, *, for_log=True):
@@ -324,36 +323,41 @@ class ElectrumX(Session):
                          for prefix, suffixes in rpcs
                          for suffix in suffixes.split()}
 
-    @classmethod
-    def notify(cls, sessions, height, touched):
-        headers_payload = height_payload = None
+    async def notify(self, height, touched, cache):
+        '''Notify the client about changes in height and touched addresses.
 
-        for session in sessions:
-            if height != session.notified_height:
-                session.notified_height = height
-                if session.subscribe_headers:
-                    if headers_payload is None:
-                        headers_payload = json_notification_payload(
-                            'blockchain.headers.subscribe',
-                            (session.electrum_header(height), ),
-                        )
-                    session.send_json(headers_payload)
+        Cache is a shared cache for this update.
+        '''
+        if height != self.notified_height:
+            self.notified_height = height
+            if self.subscribe_headers:
+                key = 'headers_payload'
+                if key not in cache:
+                    cache[key] = json_notification_payload(
+                        'blockchain.headers.subscribe',
+                        (self.electrum_header(height), ),
+                    )
+                self.send_json(cache[key])
 
-                if session.subscribe_height:
-                    if height_payload is None:
-                        height_payload = json_notification_payload(
-                            'blockchain.numblocks.subscribe',
-                            (height, ),
-                        )
-                    session.send_json(height_payload)
-
-            hash168_to_address = session.coin.hash168_to_address
-            for hash168 in session.hash168s.intersection(touched):
-                address = hash168_to_address(hash168)
-                status = session.address_status(hash168)
+            if self.subscribe_height:
                 payload = json_notification_payload(
-                    'blockchain.address.subscribe', (address, status))
-                session.send_json(payload)
+                    'blockchain.numblocks.subscribe',
+                    (height, ),
+                )
+                self.send_json(payload)
+
+        hash168_to_address = self.coin.hash168_to_address
+        matches = self.hash168s.intersection(touched)
+        for hash168 in matches:
+            address = hash168_to_address(hash168)
+            status = self.address_status(hash168)
+            payload = json_notification_payload(
+                'blockchain.address.subscribe', (address, status))
+            self.send_json(payload)
+
+        if matches:
+            self.logger.info('notified {} of {} addresses'
+                             .format(self.peername(), len(matches)))
 
     def height(self):
         '''Return the block processor's current height.'''