Implement a Redis mode

Signed-off-by: Stefano Rivera <stefano@rivera.za.net>

Author: stefanor

.github/workflows/ci.yaml

@@ -59,6 +59,9 @@ jobs:
         uses: actions/setup-python@83679a892e2d95755f2dac6acb0bfd1e9ac5d548 # v6.1.0
         with:
           python-version: ${{ matrix.python-version }}
+      - name: Install Redis
+        run: |
+          apt-get -y install redis-server
       - name: Install dependencies
         run: |
           pip install --user tox "virtualenv<20.22.0"

prometheus_client/metrics.py

@@ -207,6 +207,10 @@ def remove(self, *labelvalues: Any) -> None:
             warnings.warn(
                 "Removal of labels has not been implemented in  multi-process mode yet.",
                 UserWarning)
+        if 'PROMETHEUS_REDIS_URL' in os.environ:
+            warnings.warn(
+                "Removal of labels has not been implemented in redis mode yet.",
+                UserWarning)
 
         if not self._labelnames:
             raise ValueError('No label names were set when constructing %s' % self)
@@ -226,6 +230,10 @@ def remove_by_labels(self, labels: dict[str, str]) -> None:
                 "Removal of labels has not been implemented in  multi-process mode yet.",
                 UserWarning
             )
+        if 'PROMETHEUS_REDIS_URL' in os.environ:
+            warnings.warn(
+                "Removal of labels has not been implemented in redis mode yet.",
+                UserWarning)
 
         if not self._labelnames:
             raise ValueError('No label names were set when constructing %s' % self)
@@ -258,6 +266,10 @@ def clear(self) -> None:
             warnings.warn(
                 "Clearing labels has not been implemented in multi-process mode yet",
                 UserWarning)
+        if 'PROMETHEUS_REDIS_URL' in os.environ:
+            warnings.warn(
+                "Clearing of labels has not been implemented in redis mode yet.",
+                UserWarning)
         with self._lock:
             self._metrics = {}
 

prometheus_client/redis_collector.py

@@ -0,0 +1,107 @@
+from collections.abc import Iterable
+import json
+import os
+from urllib.parse import urlsplit
+
+from .metrics_core import Metric
+from .registry import Collector, CollectorRegistry
+from .samples import Sample
+
+
+def redis_client():
+    """
+    Create a redis client for PROMETHEUS_REDIS_URL.
+
+    Configure the redis database via a URL in PROMETHEUS_REDIS_URL of the form
+    redis://localhost:6379/0
+    """
+    from redis import Redis
+
+    parsed_url = urlsplit(os.environ["PROMETHEUS_REDIS_URL"])
+    assert parsed_url.scheme == "redis"
+    assert parsed_url.path.startswith("/")
+    assert parsed_url.path[1:].isdigit()
+    port = parsed_url.port or 6379
+    db = int(parsed_url.path[1:])
+    return Redis(host=parsed_url.hostname, port=port, db=db)
+
+
+class RedisCollector(Collector):
+    """Collector for redis mode."""
+
+    def __init__(self, registry: CollectorRegistry) -> None:
+        self._client = redis_client()
+        if registry:
+            registry.register(self)
+
+    def _iter_values(self) -> Iterable[tuple[bytes, str]]:
+        cursor = 0
+        while True:
+            cursor, keys = self._client.scan(cursor=cursor, match="value:*")
+            values = self._client.mget(keys)
+            yield from zip(keys, values)
+            if cursor == 0:
+                break
+
+    def collect(self) -> Iterable[Metric]:
+        metrics: dict[str, Metric] = {}
+        histograms: set[str] = set()
+
+        for key, value_s in self._iter_values():
+            # FIXME: Catch ValueError here, just in case?
+            prefix_b, typ_b, mmap_key = key.split(b":", 2)
+            assert prefix_b == b"value"
+            typ = typ_b.decode()
+            value = float(value_s)
+
+            metric_name, name, labels, help_text = json.loads(mmap_key)
+
+            metric = metrics.get(metric_name)
+            if metric is None:
+                metric = Metric(metric_name, help_text, typ)
+                metrics[metric_name] = metric
+                if typ in ("histogram", "gaugehistogram"):
+                    histograms.add(metric_name)
+
+            metric.add_sample(name, labels, value)
+
+        for name in histograms:
+            self._fix_histogram(metrics[name])
+
+        return metrics.values()
+
+    def _fix_histogram(self, metric: Metric) -> None:
+        """
+        Fix-up histogram samples.
+
+        Sort the buckets as expected by a client, and accumulate the values.
+        The Histogram class is optimized to only increment the bucket that a
+        value first appears in, not larger ones that would also contain it.
+        """
+        by_label: dict[tuple[tuple[str, ...], str], list[Sample]] = {}
+
+        # Organize into lists of samples by label
+        for sample in metric.samples:
+            if "le" in sample.labels:
+                labels_without_le = sample.labels.copy()
+                labels_without_le.pop("le")
+                key = (tuple(labels_without_le.values()), sample.name)
+            else:
+                key = (tuple(sample.labels.values()), sample.name)
+            by_label.setdefault(key, []).append(sample)
+
+        metric.samples = []
+
+        for (labels, name), samples in sorted(by_label.items()):
+            if name.endswith("_bucket"):
+                # Sort buckets within each label
+                samples.sort(key=lambda sample: float(sample.labels["le"]))
+
+                # Accumulate values into larger buckets
+                value = 0.0
+                for sample in samples:
+                    value += sample.value
+                    metric.samples.append(Sample(sample.name, sample.labels, value))
+
+            else:
+                metric.samples.extend(samples)

prometheus_client/values.py

@@ -1,8 +1,11 @@
 import os
 from threading import Lock
+from typing import Any
 import warnings
 
 from .mmap_dict import mmap_key, MmapedDict
+from .redis_collector import redis_client
+from .samples import Exemplar
 
 
 class MutexValue:
@@ -125,12 +128,66 @@ def get_exemplar(self):
     return MmapedValue
 
 
+def RedisValue():
+    """
+    A value implementation that stores data in a redis/valkey database.
+
+    Key scheme:
+    * value:typ:MMAP_KEY
+    """
+    client = redis_client()
+
+    class RedisValueImpl:
+        """A float stored by redis."""
+
+        _multiprocess = False
+
+        def __init__(
+            self,
+            typ: str,
+            metric_name: str,
+            name: str,
+            labelnames: list[str],
+            labelvalues: list[str],
+            help_text: str,
+            **kwargs: Any,
+        ) -> None:
+            key = mmap_key(metric_name, name, labelnames, labelvalues, help_text)
+            self._key = f"value:{typ}:{key}"
+            self._redis = client
+            self._redis.setnx(self._key, 0.0)
+
+        def inc(self, amount: float) -> None:
+            print(f"inc {self._key=} {amount=}")
+            self._redis.incrbyfloat(self._key, amount)
+
+        def set(self, value: float, timestamp: float | None = None) -> None:
+            print(f"set {self._key=} {value=}")
+            # TODO: Implement timestamps
+            self._redis.set(self._key, value)
+
+        def set_exemplar(self, exemplar: Exemplar) -> None:
+            # TODO: Implement exemplars for redis.
+            return
+
+        def get_exemplar(self) -> Exemplar | None:
+            # TODO: Implement exemplars for redis.
+            return None
+
+        def get(self) -> float:
+            return float(self._redis.get(self._key))
+
+    return RedisValueImpl
+
+
 def get_value_class():
     # Should we enable multi-process mode?
     # This needs to be chosen before the first metric is constructed,
     # and as that may be in some arbitrary library the user/admin has
     # no control over we use an environment variable.
-    if 'prometheus_multiproc_dir' in os.environ or 'PROMETHEUS_MULTIPROC_DIR' in os.environ:
+    if "PROMETHEUS_REDIS_URL" in os.environ:
+        return RedisValue()
+    elif 'prometheus_multiproc_dir' in os.environ or 'PROMETHEUS_MULTIPROC_DIR' in os.environ:
         return MultiProcessValue()
     else:
         return MutexValue

pyproject.toml

@@ -50,6 +50,9 @@ aiohttp = [
 django = [
 	"django",
 ]
+redis = [
+	"redis",
+]
 
 [project.urls]
 Homepage = "https://github.com/prometheus/client_python"