Reduce the size of the HTTP connection pool for non-pushers. (#15514)

Pushers tend to make many connections to the same HTTP host
(e.g. a new event comes in, causes events to be pushed, and then
the homeserver connects to the same host many times). Due to this
the per-host HTTP connection pool size was increased, but this does
not make sense for other SimpleHttpClients.

Add a parameter for the connection pool and override it for pushers
(making a separate SimpleHttpClient for pushers with the increased
configuration).

This returns the HTTP connection pool settings to the default Twisted
ones for non-pusher HTTP clients.

1 files changed, 21 insertions, 0 deletions

diff --git a/synapse/server.py b/synapse/server.py
index 08ad97b952..75a902d64d 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -27,6 +27,7 @@ from typing_extensions import TypeAlias
 
 from twisted.internet.interfaces import IOpenSSLContextFactory
 from twisted.internet.tcp import Port
+from twisted.web.client import HTTPConnectionPool
 from twisted.web.iweb import IPolicyForHTTPS
 from twisted.web.resource import Resource
 
@@ -454,6 +455,26 @@ class HomeServer(metaclass=abc.ABCMeta):
         )
 
     @cache_in_self
+    def get_pusher_http_client(self) -> SimpleHttpClient:
+        # the pusher makes lots of concurrent SSL connections to Sygnal, and tends to
+        # do so in batches, so we need to allow the pool to keep lots of idle
+        # connections around.
+        pool = HTTPConnectionPool(self.get_reactor())
+        # 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(int(100 * self.config.caches.global_factor), 5)
+        pool.cachedConnectionTimeout = 2 * 60
+
+        return SimpleHttpClient(
+            self,
+            ip_whitelist=self.config.server.ip_range_whitelist,
+            ip_blacklist=self.config.server.ip_range_blacklist,
+            use_proxy=True,
+            connection_pool=pool,
+        )
+
+    @cache_in_self
     def get_federation_http_client(self) -> MatrixFederationHttpClient:
         """
         An HTTP client for federation.