perf: geocode pipeline — batch POST + parallel server, 200→1 roundtrip

JS preload(): replaced N individual GET /api/geocode (concurrency 2) with
a single POST /api/geocode/batch — one HTTP roundtrip instead of up to
N/2 sequential ones. schedLoc debounce reduced 600→200ms.

Server geocode_batch(): ThreadPoolExecutor(max_workers=4) parallelises
Nominatim/reverse_geocoder calls instead of sequential loop. Deduplicates
coords before submitting futures. lru_cache absorbs duplicates within batch.

Pi geocode_batch_route(): deduplicate coords, removed stale 'if label:'
guard (label always non-empty after BUG-13 fix).

app.py

@@ -212,6 +212,9 @@ def geocode_batch_route():
     coords = body.get("coords")
     if not isinstance(coords, list) or not coords:
         return jsonify(error="expected {coords: [{lat, lon}, ...]}"), 400
+    # Deduplicate — same (lat4,lon4) would hit lru_cache anyway but avoids
+    # submitting redundant work.
+    seen = set()
     result = {}
     for item in coords:
         try:
@@ -221,9 +224,9 @@ def geocode_batch_route():
             continue
         lat4 = int(round(lat, 4) * 10000)
         lon4 = int(round(lon, 4) * 10000)
-        label = _geocode_cached(lat4, lon4)
+        if (lat4, lon4) not in seen:
-        if label:
+            seen.add((lat4, lon4))
-            result[f"{lat:.3f},{lon:.3f}"] = label
+            result[f"{lat:.3f},{lon:.3f}"] = _geocode_cached(lat4, lon4)
     return jsonify(result)
 
 @app.route('/api/dash/devices')

server/app.py

@@ -2,6 +2,7 @@
 uploaded by the Pi, storing them in Postgres + on-disk file storage.
 Also serves the remote web portal for browsing and managing the configured car.
 """
+import concurrent.futures
 import functools
 import hashlib
 import os
@@ -626,12 +627,20 @@ def geocode():
 @app.post("/api/geocode/batch")
 @require_login
 def geocode_batch():
-    """Batch geocode — returns {key: label} for all unique coords in one request."""
+    """Batch geocode — returns {key: label} for all unique coords in one request.
+
+    Parallelised with ThreadPoolExecutor (max_workers=4) so Nominatim HTTP
+    calls and reverse_geocoder lookups run concurrently instead of sequentially.
+    _geocode_cached's lru_cache absorbs duplicate coords within the batch."""
     body = request.get_json(silent=True) or {}
     coords = body.get("coords")
     if not isinstance(coords, list) or not coords:
         return jsonify(error="expected {coords: [{lat, lon}, ...]}"), 400
-    result = {}
+
+    # Deduplicate — same (lat4,lon4) would hit lru_cache anyway, but this
+    # avoids submitting redundant futures.
+    seen = set()
+    items = []
     for item in coords:
         try:
             lat = float(item["lat"])
@@ -640,9 +649,25 @@ def geocode_batch():
             continue
         lat4 = int(round(lat, 4) * 10000)
         lon4 = int(round(lon, 4) * 10000)
-        key = f"{lat:.3f},{lon:.3f}"
+        if (lat4, lon4) not in seen:
-        name = _geocode_cached(lat4, lon4)
+            seen.add((lat4, lon4))
-        result[key] = name
+            items.append((f"{lat:.3f},{lon:.3f}", lat4, lon4))
+
+    result = {}
+    if not items:
+        return jsonify(result)
+
+    with concurrent.futures.ThreadPoolExecutor(max_workers=4) as ex:
+        futures = {ex.submit(_geocode_cached, lat4, lon4): key for key, lat4, lon4 in items}
+        for future in concurrent.futures.as_completed(futures):
+            key = futures[future]
+            try:
+                result[key] = future.result(timeout=8)
+            except Exception:
+                # Last resort — raw coords if even the fallback failed
+                parts = key.split(",")
+                result[key] = f"{float(parts[0]):.5f}, {float(parts[1]):.5f}"
+
     return jsonify(result)
 
 

static/js/history.js

@@ -75,31 +75,32 @@
     function preload(pts) {
         if (_geoCtrl) _geoCtrl.abort();
         _geoCtrl = new AbortController(); var sig = _geoCtrl.signal; _cache = {};
-        var seen = {}, q = [], i;
+        var seen = {}, coords = [], i;
         for (i = 0; i < pts.length; i++) {
             var k = gk(pts[i].latitude, pts[i].longitude);
             if (!k || seen[k]) continue; seen[k] = 1;
-            q.push({k: k, lat: pts[i].latitude, lon: pts[i].longitude});
+            coords.push({lat: pts[i].latitude, lon: pts[i].longitude});
         }
-        if (!q.length) return;
+        if (!coords.length) return;
-        var C = 2, idx = 0;
+        // Single batch POST instead of N individual GETs — one roundtrip.
-        function nx() {
+        fetch("/api/geocode/batch", {
-            if (idx >= q.length || sig.aborted) return;
+            method: "POST",
-            var it = q[idx++], c = new AbortController();
+            headers: {"Content-Type": "application/json"},
-            var t = setTimeout(function () { c.abort(); }, 3000);
+            body: JSON.stringify({coords: coords}),
-            sig.addEventListener("abort", function () { c.abort(); });
+            signal: sig
-            fetch("/api/geocode?lat=" + it.lat + "&lon=" + it.lon, {signal: c.signal})
+        })
-                .then(function (r) { clearTimeout(t); return r.ok ? r.json() : null; })
+        .then(function (r) { return r.ok ? r.json() : {}; })
-                .then(function (d) { if (!sig.aborted) _cache[it.k] = (d && d.label) || null; })
+        .then(function (data) {
-                .catch(function () { clearTimeout(t); })
+            if (sig.aborted) return;
-                .finally(function () { if (!sig.aborted) nx(); });
+            for (var key in data) { if (data.hasOwnProperty(key)) _cache[key] = data[key]; }
-        }
+        })
-        for (var j = 0; j < C && j < q.length; j++) nx();
+        .catch(function () {});
     }
     function showLoc(lat, lon) {
         var k = gk(lat, lon); if (!k || k === _lastKey) return; _lastKey = k;
         var fb = lat.toFixed(5) + ", " + lon.toFixed(5);
         if (_cache.hasOwnProperty(k)) { locEl.textContent = _cache[k] || fb; return; }
+        // Fallback: individual fetch only if preload didn't cover this coord.
         var c = new AbortController();
         var t = setTimeout(function () { c.abort(); }, 3000);
         fetch("/api/geocode?lat=" + lat + "&lon=" + lon, {signal: c.signal})
@@ -112,7 +113,7 @@
     }
     function schedLoc(lat, lon) {
         clearTimeout(_geoTimer);
-        _geoTimer = setTimeout(function () { showLoc(lat, lon); }, 600);
+        _geoTimer = setTimeout(function () { showLoc(lat, lon); }, 200);
     }
 
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