Merge tag 'v1.32.1'

Synapse 1.32.1 (2021-04-21)
===========================

This release fixes [a regression](https://github.com/matrix-org/synapse/issues/9853) in Synapse 1.32.0 that caused connected Prometheus instances to become unstable. If you ran Synapse 1.32.0 with Prometheus metrics, first upgrade to Synapse 1.32.1 and follow [these instructions](https://github.com/matrix-org/synapse/pull/9854#issuecomment-823472183) to clean up any excess writeahead logs.

Bugfixes
--------

- Fix a regression in Synapse 1.32.0 which caused Synapse to report large numbers of Prometheus time series, potentially overwhelming Prometheus instances. ([\#9854](https://github.com/matrix-org/synapse/issues/9854))

1 files changed, 16 insertions, 4 deletions

diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py
index 78e9cfbc26..3f621539f3 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -16,7 +16,7 @@
 import logging
 import threading
 from functools import wraps
-from typing import TYPE_CHECKING, Dict, Optional, Set
+from typing import TYPE_CHECKING, Dict, Optional, Set, Union
 
 from prometheus_client.core import REGISTRY, Counter, Gauge
 
@@ -199,7 +199,7 @@ def run_as_background_process(desc: str, func, *args, bg_start_span=True, **kwar
         _background_process_start_count.labels(desc).inc()
         _background_process_in_flight_count.labels(desc).inc()
 
-        with BackgroundProcessLoggingContext("%s-%s" % (desc, count)) as context:
+        with BackgroundProcessLoggingContext(desc, count) as context:
             try:
                 ctx = noop_context_manager()
                 if bg_start_span:
@@ -244,8 +244,20 @@ class BackgroundProcessLoggingContext(LoggingContext):
 
     __slots__ = ["_proc"]
 
-    def __init__(self, name: str):
-        super().__init__(name)
+    def __init__(self, name: str, instance_id: Optional[Union[int, str]] = None):
+        """
+
+        Args:
+            name: The name of the background process. Each distinct `name` gets a
+                separate prometheus time series.
+
+            instance_id: an identifer to add to `name` to distinguish this instance of
+                the named background process in the logs. If this is `None`, one is
+                made up based on id(self).
+        """
+        if instance_id is None:
+            instance_id = id(self)
+        super().__init__("%s-%s" % (name, instance_id))
         self._proc = _BackgroundProcess(name, self)
 
     def start(self, rusage: "Optional[resource._RUsage]"):