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 d4844ee5aec72c5b14b7ab6540663aff56374949..9478af2c64c803a5dc274017b90bf951af39043c 100644 (file)
--- 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 3d898a447123e46a73ba2d1e0e75bf7943444b50..0b44f5a8469f94c66e7295c86570c4e8c2c700f3 100644 (file)
--- 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);
 }