rec: Add a new max-udp-queries-per-round setting

This new setting limits the number of UDP queries we attempt to
handle after being woken up by the multiplexer and before returning
back to process other events.
Before this, we could end up trying to process queries after queries
and almost never return from handleNewUDPQuestion() to process new
events, meaning we could eventually end up never scheduling new
mthreads or handle responses from authoritative servers for a long
time, only sending responses for packetcache hits and creating new
mthreads.

diff --git a/pdns/pdns_recursor.cc b/pdns/pdns_recursor.cc
index c3969996434a7ec4e27e631c5bc15677b45cefdf..4cb9df415de1bd2d5b59cdf5d6118dfb5918dcb3 100644 (file)
--- a/pdns/pdns_recursor.cc
+++ b/pdns/pdns_recursor.cc
@@ -146,6 +146,7 @@ static std::shared_ptr<SyncRes::domainmap_t> g_initialDomainMap; // new threads
 static std::shared_ptr<NetmaskGroup> g_initialAllowFrom; // new thread needs to be setup with this
 static NetmaskGroup g_XPFAcl;
 static size_t g_tcpMaxQueriesPerConn;
+static size_t s_maxUDPQueriesPerRound;
 static uint64_t g_latencyStatSize;
 static uint32_t g_disthashseed;
 static unsigned int g_maxTCPPerClient;
@@ -1996,7 +1997,7 @@ static void handleNewUDPQuestion(int fd, FDMultiplexer::funcparam_t& var)
   fromaddr.sin6.sin6_family=AF_INET6; // this makes sure fromaddr is big enough
   fillMSGHdr(&msgh, &iov, cbuf, sizeof(cbuf), data, sizeof(data), &fromaddr);
 
-  for(;;)
+  for(size_t counter = 0; counter < s_maxUDPQueriesPerRound; counter++)
   if((len=recvmsg(fd, &msgh, 0)) >= 0) {
 
     firstQuery = false;
@@ -3309,6 +3310,7 @@ static int serviceMain(int argc, char*argv[])
   g_tcpTimeout=::arg().asNum("client-tcp-timeout");
   g_maxTCPPerClient=::arg().asNum("max-tcp-per-client");
   g_tcpMaxQueriesPerConn=::arg().asNum("max-tcp-queries-per-connection");
+  s_maxUDPQueriesPerRound=::arg().asNum("max-udp-queries-per-round");
 
   if (::arg().mustDo("snmp-agent")) {
     g_snmpAgent = std::make_shared<RecursorSNMPAgent>("recursor", ::arg()["snmp-master-socket"]);
@@ -3644,6 +3646,7 @@ int main(int argc, char **argv)
     ::arg().set("max-qperq", "Maximum outgoing queries per query")="50";
     ::arg().set("max-total-msec", "Maximum total wall-clock time per query in milliseconds, 0 for unlimited")="7000";
     ::arg().set("max-recursion-depth", "Maximum number of internal recursion calls per query, 0 for unlimited")="40";
+    ::arg().set("max-udp-queries-per-round", "Maximum number of UDP queries processed per round, before returning back to normal processing")="10000";
 
     ::arg().set("include-dir","Include *.conf files from this directory")="";
     ::arg().set("security-poll-suffix","Domain name from which to query security update notifications")="secpoll.powerdns.com.";

diff --git a/pdns/recursordist/docs/settings.rst b/pdns/recursordist/docs/settings.rst
index ca19519dfb4cb4e3a11ba5a79364e5390fbd6bde..8e2004e591aed352321dae700ef0b3354cd70d6b 100644 (file)
--- a/pdns/recursordist/docs/settings.rst
+++ b/pdns/recursordist/docs/settings.rst
@@ -768,6 +768,18 @@ Maximum number of DNS queries in a TCP connection.
 
 Total maximum number of milliseconds of wallclock time the server may use to answer a single query.
 
+.. _setting-max-udp-queries-per-round:
+
+``max-udp-queries-per-round``
+----------------------------------
+.. versionadded:: 4.2.0
+
+-  Integer
+-  Default: 10000
+
+Maximum number of DNS queries processed in a single round after being woken up by the multiplexer, before
+returning back to normal processing to handle other events.
+
 .. _setting-minimum-ttl-override:
 
 ``minimum-ttl-override``