From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Mon, 22 Mar 2021 17:45:01 +0000 (+0100)
Subject: dnsdist: Add setMaxCachedTCPConnectionsPerDownstream()
X-Git-Tag: rec-4.6.0-alpha0~1^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6d26db15c28a56b149d2a18f24ca239127e62bf3;p=thirdparty%2Fpdns.git

dnsdist: Add setMaxCachedTCPConnectionsPerDownstream()
---

diff --git a/pdns/dnsdist-console.cc b/pdns/dnsdist-console.cc
index f4dfd2c8d6..c3bd5e20c4 100644
--- a/pdns/dnsdist-console.cc
+++ b/pdns/dnsdist-console.cc
@@ -586,6 +586,7 @@ const std::vector<ConsoleKeyword> g_consoleKeywords{
   { "setECSSourcePrefixV6", true, "prefix-length", "the EDNS Client Subnet prefix-length used for IPv6 queries" },
   { "setKey", true, "key", "set access key to that key" },
   { "setLocal", true, "addr [, {doTCP=true, reusePort=false, tcpFastOpenQueueSize=0, interface=\"\", cpus={}}]", "reset the list of addresses we listen on to this address" },
+  { "setMaxCachedTCPConnectionsPerDownstream", true, "max", "Set the maximum number of inactive TCP connections to a backend cached by each worker TCP thread" },
   { "setMaxTCPClientThreads", true, "n", "set the maximum of TCP client threads, handling TCP connections" },
   { "setMaxTCPConnectionDuration", true, "n", "set the maximum duration of an incoming TCP connection, in seconds. 0 means unlimited" },
   { "setMaxTCPConnectionsPerClient", true, "n", "set the maximum number of TCP connections per client. 0 means unlimited" },
diff --git a/pdns/dnsdist-lua.cc b/pdns/dnsdist-lua.cc
index de3fbe701b..f234741d80 100644
--- a/pdns/dnsdist-lua.cc
+++ b/pdns/dnsdist-lua.cc
@@ -1188,6 +1188,10 @@ static void setupLuaConfig(LuaContext& luaCtx, bool client, bool configCheck)
       }
     });
 
+  luaCtx.writeFunction("setMaxCachedTCPConnectionsPerDownstream", [](size_t max) {
+    setMaxCachedTCPConnectionsPerDownstream(max);
+    });
+
   luaCtx.writeFunction("setCacheCleaningDelay", [](uint32_t delay) { g_cacheCleaningDelay = delay; });
 
   luaCtx.writeFunction("setCacheCleaningPercentage", [](uint16_t percentage) { if (percentage < 100) g_cacheCleaningPercentage = percentage; else g_cacheCleaningPercentage = 100; });
diff --git a/pdns/dnsdist-tcp.cc b/pdns/dnsdist-tcp.cc
index 19185d9d53..c52015021b 100644
--- a/pdns/dnsdist-tcp.cc
+++ b/pdns/dnsdist-tcp.cc
@@ -127,13 +127,12 @@ public:
 
     const auto& ds = conn->getDS();
     auto& list = t_downstreamConnections[ds];
-    if (list.size() >= s_maxCachedConnectionsPerDownstream) {
+    while (list.size() >= s_maxCachedConnectionsPerDownstream) {
       /* too many connections queued already */
-      conn.reset();
-    }
-    else {
-      list.push_back(std::move(conn));
+      list.pop_front();
     }
+
+    list.push_back(std::move(conn));
   }
 
   static void cleanupClosedTCPConnections(struct timeval now)
@@ -183,13 +182,23 @@ public:
     return count;
   }
 
+  static void setMaxCachedConnectionsPerDownstream(size_t max)
+  {
+    s_maxCachedConnectionsPerDownstream = max;
+  }
+
 private:
   static thread_local map<std::shared_ptr<DownstreamState>, std::deque<std::shared_ptr<TCPConnectionToBackend>>> t_downstreamConnections;
-  static const size_t s_maxCachedConnectionsPerDownstream;
+  static size_t s_maxCachedConnectionsPerDownstream;
 };
 
+void setMaxCachedTCPConnectionsPerDownstream(size_t max)
+{
+  DownstreamConnectionsManager::setMaxCachedConnectionsPerDownstream(max);
+}
+
 thread_local map<std::shared_ptr<DownstreamState>, std::deque<std::shared_ptr<TCPConnectionToBackend>>> DownstreamConnectionsManager::t_downstreamConnections;
-const size_t DownstreamConnectionsManager::s_maxCachedConnectionsPerDownstream{20};
+size_t DownstreamConnectionsManager::s_maxCachedConnectionsPerDownstream{10};
 
 static void decrementTCPClientCount(const ComboAddress& client)
 {
diff --git a/pdns/dnsdist.hh b/pdns/dnsdist.hh
index 434647a3df..a9ecda0a06 100644
--- a/pdns/dnsdist.hh
+++ b/pdns/dnsdist.hh
@@ -1229,6 +1229,8 @@ struct LocalHolders
 vector<std::function<void(void)>> setupLua(bool client, const std::string& config);
 
 void tcpAcceptorThread(ClientState* p);
+void setMaxCachedTCPConnectionsPerDownstream(size_t max);
+
 #ifdef HAVE_DNS_OVER_HTTPS
 void dohThread(ClientState* cs);
 #endif /* HAVE_DNS_OVER_HTTPS */
diff --git a/pdns/dnsdistdist/docs/reference/tuning.rst b/pdns/dnsdistdist/docs/reference/tuning.rst
index 49fccdcb68..e483bf2990 100644
--- a/pdns/dnsdistdist/docs/reference/tuning.rst
+++ b/pdns/dnsdistdist/docs/reference/tuning.rst
@@ -1,6 +1,14 @@
 Tuning related functions
 ========================
 
+.. function:: setMaxCachedTCPConnectionsPerDownstream(max)
+
+  .. versionadded:: 1.6.0
+
+  Set the maximum number of inactive TCP connections to a backend cached by each TCP worker thread. These connections can be reused when a new query comes in, instead of having to establish a new connection. dnsdist regularly checks whether the other end has closed any cached connection, closing them in that case.
+
+  :param int max: The maximum number of inactive connections to keep. Default is 10, so 10 connections per backend and per TCP worker thread.
+
 .. function:: setMaxTCPClientThreads(num)
 
   .. versionchanged:: 1.6.0