Allow configuration of Synapse's cache without using synctl or environment variables

changelog.d/6391.feature

@@ -0,0 +1 @@
+Synapse's cache factor can now be configured in `homeserver.yaml` by the `caches.global_factor` setting. Additionally, `caches.per_cache_factors` controls the cache factors for individual caches.

docs/sample_config.yaml

@@ -591,6 +591,45 @@ acme:
 
 
 
+## Caching ##
+
+# Caching can be configured through the following options.
+#
+# A cache 'factor' is a multiplier that can be applied to each of
+# Synapse's caches in order to increase or decrease the maximum
+# number of entries that can be stored.
+
+# The number of events to cache in memory. Not affected by
+# caches.global_factor.
+#
+#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
+   #
+   per_cache_factors:
+     #get_users_who_share_room_with_user: 2.0
+
+
 ## Database ##
 
 # The 'database' setting defines the database that synapse uses to store all of
@@ -634,10 +673,6 @@ database:
   args:
     database: DATADIR/homeserver.db
 
-# Number of events to cache in memory.
-#
-#event_cache_size: 10K
-
 
 ## Logging ##
 

synapse/api/auth.py

@@ -38,7 +38,7 @@
 from synapse.config.server import is_threepid_reserved
 from synapse.events import EventBase
 from synapse.types import StateMap, UserID
-from synapse.util.caches import CACHE_SIZE_FACTOR, register_cache
+from synapse.util.caches import register_cache
 from synapse.util.caches.lrucache import LruCache
 from synapse.util.metrics import Measure
 
@@ -74,7 +74,7 @@ def __init__(self, hs):
         self.store = hs.get_datastore()
         self.state = hs.get_state_handler()
 
-        self.token_cache = LruCache(CACHE_SIZE_FACTOR * 10000)
+        self.token_cache = LruCache(10000)
         register_cache("cache", "token_cache", self.token_cache)
 
         self._account_validity = hs.config.account_validity

synapse/app/homeserver.py

@@ -69,7 +69,6 @@
 from synapse.storage import DataStore
 from synapse.storage.engines import IncorrectDatabaseSetup
 from synapse.storage.prepare_database import UpgradeDatabaseException
-from synapse.util.caches import CACHE_SIZE_FACTOR
 from synapse.util.httpresourcetree import create_resource_tree
 from synapse.util.manhole import manhole
 from synapse.util.module_loader import load_module
@@ -504,8 +503,8 @@ def phone_stats_home(hs, stats, stats_process=_stats_process):
 
     daily_sent_messages = yield hs.get_datastore().count_daily_sent_messages()
     stats["daily_sent_messages"] = daily_sent_messages
-    stats["cache_factor"] = CACHE_SIZE_FACTOR
-    stats["event_cache_size"] = hs.config.event_cache_size
+    stats["cache_factor"] = hs.config.caches.global_factor
+    stats["event_cache_size"] = hs.config.caches.event_cache_size
 
     #
     # Performance statistics

synapse/config/cache.py

@@ -0,0 +1,164 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+from typing import Callable, Dict
+
+from ._base import Config, ConfigError
+
+# The prefix for all cache factor-related environment variables
+_CACHES = {}
+_CACHE_PREFIX = "SYNAPSE_CACHE_FACTOR"
+_DEFAULT_FACTOR_SIZE = 0.5
+_DEFAULT_EVENT_CACHE_SIZE = "10K"
+
+
+class CacheProperties(object):
+    def __init__(self):
+        # The default factor size for all caches
+        self.default_factor_size = float(
+            os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
+        )
+        self.resize_all_caches_func = None
+
+
+properties = CacheProperties()
+
+
+def add_resizable_cache(cache_name: str, cache_resize_callback: Callable):
+    """Register a cache that's size can dynamically change
+
+    Args:
+        cache_name: A reference to the cache
+        cache_resize_callback: A callback function that will be ran whenever
+            the cache needs to be resized
+    """
+    _CACHES[cache_name.lower()] = cache_resize_callback
+
+    # Ensure all loaded caches are sized appropriately
+    #
+    # This method should only run once the config has been read,
+    # as it uses values read from it
+    if properties.resize_all_caches_func:
+        properties.resize_all_caches_func()
+
+
+class CacheConfig(Config):
+    section = "caches"
+    _environ = os.environ
+
+    @staticmethod
+    def reset():
+        """Resets the caches to their defaults. Used for tests."""
+        properties.default_factor_size = float(
+            os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
+        )
+        properties.resize_all_caches_func = None
+        _CACHES.clear()
+
+    def generate_config_section(self, **kwargs):
+        return """\
+        ## Caching ##
+
+        # Caching can be configured through the following options.
+        #
+        # A cache 'factor' is a multiplier that can be applied to each of
+        # Synapse's caches in order to increase or decrease the maximum
+        # number of entries that can be stored.
+
+        # The number of events to cache in memory. Not affected by
+        # caches.global_factor.
+        #
+        #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
+           #
+           per_cache_factors:
+             #get_users_who_share_room_with_user: 2.0
+        """
+
+    def read_config(self, config, **kwargs):
+        self.event_cache_size = self.parse_size(
+            config.get("event_cache_size", _DEFAULT_EVENT_CACHE_SIZE)
+        )
+        self.cache_factors = {}  # type: Dict[str, float]
+
+        cache_config = config.get("caches") or {}
+        self.global_factor = cache_config.get(
+            "global_factor", properties.default_factor_size
+        )
+        if not isinstance(self.global_factor, (int, float)):
+            raise ConfigError("caches.global_factor must be a number.")
+
+        # Set the global one so that it's reflected in new caches
+        properties.default_factor_size = self.global_factor
+
+        # Load cache factors from the config
+        individual_factors = cache_config.get("per_cache_factors") or {}
+        if not isinstance(individual_factors, dict):
+            raise ConfigError("caches.per_cache_factors must be a dictionary")
+
+        # Override factors from environment if necessary
+        individual_factors.update(
+            {
+                key[len(_CACHE_PREFIX) + 1 :].lower(): float(val)
+                for key, val in self._environ.items()
+                if key.startswith(_CACHE_PREFIX + "_")
+            }
+        )
+
+        for cache, factor in individual_factors.items():
+            if not isinstance(factor, (int, float)):
+                raise ConfigError(
+                    "caches.per_cache_factors.%s must be a number" % (cache.lower(),)
+                )
+            self.cache_factors[cache.lower()] = factor
+
+        # Resize all caches (if necessary) with the new factors we've loaded
+        self.resize_all_caches()
+
+        # Store this function so that it can be called from other classes without
+        # needing an instance of Config
+        properties.resize_all_caches_func = self.resize_all_caches
+
+    def resize_all_caches(self):
+        """Ensure all cache sizes are up to date
+
+        For each cache, run the mapped callback function with either
+        a specific cache factor or the default, global one.
+        """
+        for cache_name, callback in _CACHES.items():
+            new_factor = self.cache_factors.get(cache_name, self.global_factor)
+            callback(new_factor)

synapse/config/database.py

@@ -68,10 +68,6 @@
   name: sqlite3
   args:
     database: %(database_path)s
-
-# Number of events to cache in memory.
-#
-#event_cache_size: 10K
 """
 
 
@@ -116,8 +112,6 @@ def __init__(self, *args, **kwargs):
         self.databases = []
 
     def read_config(self, config, **kwargs):
-        self.event_cache_size = self.parse_size(config.get("event_cache_size", "10K"))
-
         # We *experimentally* support specifying multiple databases via the
         # `databases` key. This is a map from a label to database config in the
         # same format as the `database` config option, plus an extra

synapse/config/homeserver.py

@@ -17,6 +17,7 @@
 from ._base import RootConfig
 from .api import ApiConfig
 from .appservice import AppServiceConfig
+from .cache import CacheConfig
 from .captcha import CaptchaConfig
 from .cas import CasConfig
 from .consent_config import ConsentConfig
@@ -54,6 +55,7 @@ class HomeServerConfig(RootConfig):
     config_classes = [
         ServerConfig,
         TlsConfig,
+        CacheConfig,
         DatabaseConfig,
         LoggingConfig,
         RatelimitConfig,

synapse/http/client.py

@@ -49,7 +49,6 @@
 from synapse.logging.context import make_deferred_yieldable
 from synapse.logging.opentracing import set_tag, start_active_span, tags
 from synapse.util.async_helpers import timeout_deferred
-from synapse.util.caches import CACHE_SIZE_FACTOR
 
 logger = logging.getLogger(__name__)
 
@@ -241,7 +240,10 @@ def __getattr__(_self, attr):
         # tends to do so in batches, so we need to allow the pool to keep
         # lots of idle connections around.
         pool = HTTPConnectionPool(self.reactor)
-        pool.maxPersistentPerHost = max((100 * CACHE_SIZE_FACTOR, 5))
+        # XXX: The justification for using the cache factor here is that larger instances
+        # will need both more cache and more connections.
+        # Still, this should probably be a separate dial
+        pool.maxPersistentPerHost = max((100 * hs.config.caches.global_factor, 5))
         pool.cachedConnectionTimeout = 2 * 60
 
         self.agent = ProxyAgent(

synapse/metrics/_exposition.py

@@ -33,6 +33,8 @@
 
 from twisted.web.resource import Resource
 
+from synapse.util import caches
+
 try:
     from prometheus_client.samples import Sample
 except ImportError:
@@ -103,13 +105,15 @@ def nameify_sample(sample):
 
 
 def generate_latest(registry, emit_help=False):
-    output = []
 
-    for metric in registry.collect():
+    # Trigger the cache metrics to be rescraped, which updates the common
+    # metrics but do not produce metrics themselves
+    for collector in caches.collectors_by_name.values():
+        collector.collect()
 
-        if metric.name.startswith("__unused"):
-            continue
+    output = []
 
+    for metric in registry.collect():
         if not metric.samples:
             # No samples, don't bother.
             continue

synapse/push/bulk_push_rule_evaluator.py

@@ -51,6 +51,7 @@
     "cache",
     "push_rules_delta_state_cache_metric",
     cache=[],  # Meaningless size, as this isn't a cache that stores values
+    resizable=False,
 )
 
 
@@ -67,7 +68,8 @@ def __init__(self, hs):
         self.room_push_rule_cache_metrics = register_cache(
             "cache",
             "room_push_rule_cache",
-            cache=[],  # Meaningless size, as this isn't a cache that stores values
+            cache=[],  # Meaningless size, as this isn't a cache that stores values,
+            resizable=False,
         )
 
     @defer.inlineCallbacks

synapse/push/push_rule_evaluator.py

@@ -22,7 +22,7 @@
 
 from synapse.events import EventBase
 from synapse.types import UserID
-from synapse.util.caches import CACHE_SIZE_FACTOR, register_cache
+from synapse.util.caches import register_cache
 from synapse.util.caches.lrucache import LruCache
 
 logger = logging.getLogger(__name__)
@@ -165,7 +165,7 @@ def _get_value(self, dotted_key: str) -> str:
 
 
 # Caches (string, is_glob, word_boundary) -> regex for push. See _glob_matches
-regex_cache = LruCache(50000 * CACHE_SIZE_FACTOR)
+regex_cache = LruCache(50000)
 register_cache("cache", "regex_push_cache", regex_cache)
 
 

synapse/replication/slave/storage/client_ips.py

@@ -15,7 +15,6 @@
 
 from synapse.storage.data_stores.main.client_ips import LAST_SEEN_GRANULARITY
 from synapse.storage.database import Database
-from synapse.util.caches import CACHE_SIZE_FACTOR
 from synapse.util.caches.descriptors import Cache
 
 from ._base import BaseSlavedStore
@@ -26,7 +25,7 @@ def __init__(self, database: Database, db_conn, hs):
         super(SlavedClientIpStore, self).__init__(database, db_conn, hs)
 
         self.client_ip_last_seen = Cache(
-            name="client_ip_last_seen", keylen=4, max_entries=50000 * CACHE_SIZE_FACTOR
+            name="client_ip_last_seen", keylen=4, max_entries=50000
         )
 
     def insert_client_ip(self, user_id, access_token, ip, user_agent, device_id):