From 301779cf0964a972a7f70b9c3270d7cbb3e77480 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Mon, 6 Apr 2020 15:05:37 +0200
Subject: [PATCH] auth: Add a new 'backend-queries' metric

Counting the numbers of queries sent to the backend(s), instead of
relying on the number of cache misses.
---
 pdns/dnsbackend.cc                          |  4 ++++
 pdns/ueberbackend.cc                        | 11 ++++++++---
 pdns/ueberbackend.hh                        |  1 +
 regression-tests.nobackend/counters/command |  2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/pdns/dnsbackend.cc b/pdns/dnsbackend.cc
index 07fe9c6d42f4..9113d966a5ac 100644
--- a/pdns/dnsbackend.cc
+++ b/pdns/dnsbackend.cc
@@ -32,6 +32,9 @@
 #include "pdns/packetcache.hh"
 #include "dnspacket.hh"
 #include "dns.hh"
+#include "statbag.hh"
+
+extern StatBag S;
 
 // this has to be somewhere central, and not in a file that requires Lua
 // this is so the geoipbackend can set this pointer if loaded for lua-record.cc
@@ -223,6 +226,7 @@ vector<DNSBackend *>BackendMakerClass::all(bool metadataOnly)
 bool DNSBackend::getSOA(const DNSName &domain, SOAData &sd)
 {
   this->lookup(QType(QType::SOA),domain,-1);
+  S.inc("backend-queries");
 
   DNSResourceRecord rr;
   rr.auth = true;
diff --git a/pdns/ueberbackend.cc b/pdns/ueberbackend.cc
index 24af24c4ca79..3282b5567f64 100644
--- a/pdns/ueberbackend.cc
+++ b/pdns/ueberbackend.cc
@@ -50,10 +50,11 @@
 extern StatBag S;
 
 vector<UeberBackend *>UeberBackend::instances;
-pthread_mutex_t UeberBackend::instances_lock=PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t UeberBackend::instances_lock = PTHREAD_MUTEX_INITIALIZER;
 
 // initially we are blocked
-bool UeberBackend::d_go=false;
+bool UeberBackend::d_go = false;
+AtomicCounter* UeberBackend::s_backendQueries = nullptr;
 pthread_mutex_t  UeberBackend::d_mut = PTHREAD_MUTEX_INITIALIZER;
 pthread_cond_t UeberBackend::d_cond = PTHREAD_COND_INITIALIZER;
 
@@ -95,7 +96,9 @@ bool UeberBackend::loadModules(const vector<string>& modules, const string& path
 void UeberBackend::go(void)
 {
   pthread_mutex_lock(&d_mut);
-  d_go=true;
+  d_go = true;
+  S.declare("backend-queries", "Number of queries sent to the backend(s)");
+  s_backendQueries = S.getPointer("backend-queries");
   pthread_cond_broadcast(&d_cond);
   pthread_mutex_unlock(&d_mut);
 }
@@ -632,6 +635,7 @@ void UeberBackend::lookup(const QType &qtype,const DNSName &qname, int zoneId, D
       d_answers.clear();
       d_handle.d_hinterBackend = backends.at(d_handle.i++);
       d_handle.d_hinterBackend->lookup(QType::ANY, qname, zoneId, pkt_p);
+      ++(*s_backendQueries);
     } 
     else if (cstat == 0) {
       //      cout<<"UeberBackend::lookup("<<qname<<"|"<<DNSRecordContent::NumberToType(qtype.getCode())<<"): NEGcached"<<endl;
@@ -755,6 +759,7 @@ bool UeberBackend::handle::get(DNSZoneRecord &r)
       
       d_hinterBackend = parent->backends.at(i++);
       d_hinterBackend->lookup(qtype, qname, parent->d_domain_id, pkt_p);
+      ++(*s_backendQueries);
     }
     else {
       break;
diff --git a/pdns/ueberbackend.hh b/pdns/ueberbackend.hh
index b4b5427c7255..e8a5aa126a46 100644
--- a/pdns/ueberbackend.hh
+++ b/pdns/ueberbackend.hh
@@ -158,6 +158,7 @@ private:
   bool d_cached{false};
   bool d_stale{false};
 
+  static AtomicCounter* s_backendQueries;
   static bool d_go;
 
   int cacheHas(const Question &q, vector<DNSZoneRecord> &rrs);
diff --git a/regression-tests.nobackend/counters/command b/regression-tests.nobackend/counters/command
index 9ff54727d7c9..91ef56e8dce5 100755
--- a/regression-tests.nobackend/counters/command
+++ b/regression-tests.nobackend/counters/command
@@ -27,7 +27,7 @@ $SDIG ::1 $port example.com SOA >&2 >/dev/null
 $SDIG ::1 $port example.com SOA tcp >&2 >/dev/null
 
 $PDNSCONTROL --config-name= --no-config --socket-dir=./ 'show *' | \
-  tr ',' '\n'| grep -v -E '(user-msec|sys-msec|cpu-iowait|cpu-steal|uptime|udp-noport-errors|udp-in-errors|real-memory-usage|special-memory-usage|udp-recvbuf-errors|udp-sndbuf-errors|-hit|-miss|fd-usage|latency)' | LC_ALL=C sort
+  tr ',' '\n'| grep -v -E '(user-msec|sys-msec|cpu-iowait|cpu-steal|uptime|udp-noport-errors|udp-in-errors|real-memory-usage|special-memory-usage|udp-recvbuf-errors|udp-sndbuf-errors|-hit|-miss|fd-usage|latency|backend-queries)' | LC_ALL=C sort
 
 kill $(cat pdns*.pid)
 rm pdns*.pid