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

@@ -673,35 +673,41 @@ retention:
 #event_cache_size: 10K
 
 caches:
-   # Controls the global cache factor, which is the default cache factor
-   # for all caches if a specific factor for that cache is not otherwise
-   # set.
-   #
-   # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
-   # variable. Setting by environment variable takes priority over
-   # setting through the config file.
-   #
-   # Defaults to 0.5, which will half the size of all caches.
-   #
-   #global_factor: 1.0
+    # Controls the global cache factor, which is the default cache factor
+    # for all caches if a specific factor for that cache is not otherwise
+    # set.
+    #
+    # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
+    # variable. Setting by environment variable takes priority over
+    # setting through the config file.
+    #
+    # Defaults to 0.5, which will half the size of all caches.
+    #
+    #global_factor: 1.0
 
-   # A dictionary of cache name to cache factor for that individual
-   # cache. Overrides the global cache factor for a given cache.
-   #
-   # These can also be set through environment variables comprised
-   # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
-   # letters and underscores. Setting by environment variable
-   # takes priority over setting through the config file.
-   # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
-   #
-   # Some caches have '*' and other characters that are not
-   # alphanumeric or underscores. These caches can be named with or
-   # without the special characters stripped. For example, to specify
-   # the cache factor for `*stateGroupCache*` via an environment
-   # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2.0`.
-   #
-   per_cache_factors:
-     #get_users_who_share_room_with_user: 2.0
+    # A dictionary of cache name to cache factor for that individual
+    # cache. Overrides the global cache factor for a given cache.
+    #
+    # These can also be set through environment variables comprised
+    # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
+    # letters and underscores. Setting by environment variable
+    # takes priority over setting through the config file.
+    # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
+    #
+    # Some caches have '*' and other characters that are not
+    # alphanumeric or underscores. These caches can be named with or
+    # without the special characters stripped. For example, to specify
+    # the cache factor for `*stateGroupCache*` via an environment
+    # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2.0`.
+    #
+    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

@@ -116,35 +116,41 @@ def generate_config_section(self, **kwargs):
         #event_cache_size: 10K
 
         caches:
-           # Controls the global cache factor, which is the default cache factor
-           # for all caches if a specific factor for that cache is not otherwise
-           # set.
-           #
-           # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
-           # variable. Setting by environment variable takes priority over
-           # setting through the config file.
-           #
-           # Defaults to 0.5, which will half the size of all caches.
-           #
-           #global_factor: 1.0
-
-           # A dictionary of cache name to cache factor for that individual
-           # cache. Overrides the global cache factor for a given cache.
-           #
-           # These can also be set through environment variables comprised
-           # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
-           # letters and underscores. Setting by environment variable
-           # takes priority over setting through the config file.
-           # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
-           #
-           # Some caches have '*' and other characters that are not
-           # alphanumeric or underscores. These caches can be named with or
-           # without the special characters stripped. For example, to specify
-           # the cache factor for `*stateGroupCache*` via an environment
-           # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2.0`.
-           #
-           per_cache_factors:
-             #get_users_who_share_room_with_user: 2.0
+            # Controls the global cache factor, which is the default cache factor
+            # for all caches if a specific factor for that cache is not otherwise
+            # set.
+            #
+            # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
+            # variable. Setting by environment variable takes priority over
+            # setting through the config file.
+            #
+            # Defaults to 0.5, which will half the size of all caches.
+            #
+            #global_factor: 1.0
+
+            # A dictionary of cache name to cache factor for that individual
+            # cache. Overrides the global cache factor for a given cache.
+            #
+            # These can also be set through environment variables comprised
+            # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
+            # letters and underscores. Setting by environment variable
+            # takes priority over setting through the config file.
+            # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
+            #
+            # Some caches have '*' and other characters that are not
+            # alphanumeric or underscores. These caches can be named with or
+            # without the special characters stripped. For example, to specify
+            # the cache factor for `*stateGroupCache*` via an environment
+            # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2.0`.
+            #
+            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")
+        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()