Add support for evicting cache entries based on last access time.

changelog.d/10205.feature

@@ -0,0 +1 @@
+Add support for evicting cache entries based on last access time.

docs/sample_config.yaml

@@ -703,6 +703,12 @@ caches:
    per_cache_factors:
      #get_users_who_share_room_with_user: 2.0
 
+    # Controls how long an entry can be in a cache without having been
+    # accessed before being evicted. Defaults to None, which means
+    # entries are never evicted based on time.
+    #
+    #expiry_time: 30m
+
 
 ## Database ##
 

synapse/app/_base.py

@@ -21,7 +21,7 @@
 import sys
 import traceback
 import warnings
-from typing import Awaitable, Callable, Iterable
+from typing import TYPE_CHECKING, Awaitable, Callable, Iterable
 
 from cryptography.utils import CryptographyDeprecationWarning
 from typing_extensions import NoReturn
@@ -41,10 +41,14 @@
 from synapse.logging.context import PreserveLoggingContext
 from synapse.metrics.background_process_metrics import wrap_as_background_process
 from synapse.metrics.jemalloc import setup_jemalloc_stats
+from synapse.util.caches.lrucache import setup_expire_lru_cache_entries
 from synapse.util.daemonize import daemonize_process
 from synapse.util.rlimit import change_resource_limit
 from synapse.util.versionstring import get_version_string
 
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 logger = logging.getLogger(__name__)
 
 # list of tuples of function, args list, kwargs dict
@@ -312,7 +316,7 @@ def refresh_certificate(hs):
         logger.info("Context factories updated.")
 
 
-async def start(hs: "synapse.server.HomeServer"):
+async def start(hs: "HomeServer"):
     """
     Start a Synapse server or worker.
 
@@ -365,6 +369,9 @@ def run_sighup(*args, **kwargs):
 
     load_legacy_spam_checkers(hs)
 
+    # If we've configured an expiry time for caches, start the background job now.
+    setup_expire_lru_cache_entries(hs)
+
     # It is now safe to start your Synapse.
     hs.start_listening()
     hs.get_datastore().db_pool.start_profiling()

synapse/config/_base.pyi

@@ -5,6 +5,7 @@ from synapse.config import (
     api,
     appservice,
     auth,
+    cache,
     captcha,
     cas,
     consent,
@@ -88,6 +89,7 @@ class RootConfig:
     tracer: tracer.TracerConfig
     redis: redis.RedisConfig
     modules: modules.ModulesConfig
+    caches: cache.CacheConfig
     federation: federation.FederationConfig
 
     config_classes: List = ...

synapse/config/cache.py

@@ -145,6 +145,12 @@ def generate_config_section(self, **kwargs):
            #
            per_cache_factors:
              #get_users_who_share_room_with_user: 2.0
+
+            # Controls how long an entry can be in a cache without having been
+            # accessed before being evicted. Defaults to None, which means
+            # entries are never evicted based on time.
+            #
+            #expiry_time: 30m
         """
 
     def read_config(self, config, **kwargs):
@@ -200,6 +206,12 @@ def read_config(self, config, **kwargs):
                     e.message  # noqa: B306, DependencyException.message is a property
                 )
 
+        expiry_time = cache_config.get("expiry_time", None)
+        if expiry_time:
+            self.expiry_time_msec = self.parse_duration(expiry_time)
+        else:
+            self.expiry_time_msec = None
+
         # Resize all caches (if necessary) with the new factors we've loaded
         self.resize_all_caches()