From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Wed, 24 Feb 2016 16:13:14 +0000 (+0100)
Subject: recursor: Move replaced cached entries to the back
X-Git-Tag: rec-4.0.0-alpha2~60^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fpull%2F3451%2Fhead;p=thirdparty%2Fpdns.git

recursor: Move replaced cached entries to the back

When we replace an existing entry, it keeps its existing place in
the expunge queue, while new entries are inserted to the back and
hits are moved to the back.
Moving replaced entries to the back of the queue is more fair and
so probably more efficient, as it would increase the likelihood of
expunging unused expired entries from the cache.
---

diff --git a/pdns/recpacketcache.cc b/pdns/recpacketcache.cc
index d4844ee5ae..9478af2c64 100644
--- a/pdns/recpacketcache.cc
+++ b/pdns/recpacketcache.cc
@@ -126,6 +126,7 @@ void RecursorPacketCache::insertResponsePacket(unsigned int tag, const DNSName&
     DNSName respname(iter->d_packet.c_str(), iter->d_packet.length(), sizeof(dnsheader), false, 0, 0, 0);
     if(qname != respname)
       continue;
+    moveCacheItemToBack(d_packetCache, iter);
     iter->d_packet = responsePacket;
     iter->d_ttd = now + ttl;
     iter->d_creation = now;
diff --git a/pdns/recursor_cache.cc b/pdns/recursor_cache.cc
index 3d898a4471..0b44f5a846 100644
--- a/pdns/recursor_cache.cc
+++ b/pdns/recursor_cache.cc
@@ -127,10 +127,12 @@ void MemRecursorCache::replace(time_t now, const DNSName &qname, const QType& qt
   d_cachecachevalid=false;
 
   cache_t::iterator stored;
+  bool isNew = false;
   auto key=boost::make_tuple(qname, qt.getCode(), ednsmask ? *ednsmask : Netmask());
   stored=d_cache.find(key);
   if(stored == d_cache.end()) {
     stored=d_cache.insert(CacheEntry(key,CacheEntry::records_t(), auth)).first;
+    isNew = true;
   }
 
   uint32_t maxTTD=UINT_MAX;
@@ -174,6 +176,9 @@ void MemRecursorCache::replace(time_t now, const DNSName &qname, const QType& qt
     // there was code here that did things with TTL and auth. Unsure if it was good. XXX
   }
 
+  if (!isNew) {
+    moveCacheItemToBack(d_cache, stored);
+  }
   d_cache.replace(stored, ce);
 }