fix/feat: register metrics only once andd add hit-miss

cashews/contrib/prometheus.py

@@ -1,29 +1,41 @@
 from typing import Optional
 
-from prometheus_client import Histogram
+from prometheus_client import Histogram, Counter
 
 from cashews import cache
 from cashews._typing import Middleware
 from cashews.backends.interface import Backend
 from cashews.commands import Command
 
+_DEFAULT_METRIC = Histogram(
+    "cashews_operations_latency_seconds",
+    "Latency of different operations with a cache",
+    labelnames=["operation", "backend_class", "tag"],
+)
+_HIT_MISS = Counter(
+    "cashews_get_operation",
+    "Count of hits or missed GET operations",
+    labelnames=["result", "backend_class", "tag"],
+)
 
-def create_metrics_middleware(latency_metric: Optional[Histogram] = None, with_tag: bool = False) -> Middleware:
-    _DEFAULT_METRIC = Histogram(
-        "cashews_operations_latency_seconds",
-        "Latency of different operations with a cache",
-        labelnames=["operation", "backend_class"] if not with_tag else ["operation", "backend_class", "tag"],
-    )
-    _latency_metric = latency_metric or _DEFAULT_METRIC
+
+def create_metrics_middleware(with_tag: bool = False) -> Middleware:
 
     async def metrics_middleware(call, cmd: Command, backend: Backend, *args, **kwargs):
-        with _latency_metric.time() as metric:
-            metric.labels(operation=cmd.value, backend_class=backend.__class__.__name__)
+        with _DEFAULT_METRIC.time() as metric:
+            tag = ""
+
             if with_tag and "key" in kwargs:
                 tags = cache.get_key_tags(kwargs["key"])
-                tag = next((t for t in tags), None)
-                if tag:
-                    metric.labels(tag=tag)
-            return await call(*args, **kwargs)
+                tag = next((t for t in tags), "")
+            metric.labels(operation=cmd.value, backend_class=backend.__class__.__name__, tag=tag)
+            result = await call(*args, **kwargs)
+            if cmd is Command.GET:
+                if result is not kwargs["default"]:
+                    op_result = "hit"
+                else:
+                    op_result = "miss"
+                _HIT_MISS.labels(result=op_result, backend_class=backend.__class__.__name__, tag=tag).inc()
+            return result
 
     return metrics_middleware

cashews/wrapper/wrapper.py

@@ -76,7 +76,7 @@ def _check_setup(self) -> None:
     def _add_backend(self, backend: Backend, middlewares=(), prefix: str = default_prefix) -> None:
         self._backends[prefix] = (
             backend,
-            tuple(self._default_middlewares) + middlewares,
+            middlewares + tuple(self._default_middlewares),
         )
 
     async def init(self, *args, **kwargs) -> None: