amend! Reduce QPDB_VIRTUAL to 30 seconds

Reduce QPDB_VIRTUAL to 10 seconds

The *DB_VIRTUAL value was introduced to allow the clients (presumably
ns_clients) that has been running for some time to access the cached
data that was valid at the time of its inception.  The default value
of 5 minutes is way longer than longevity of the ns_client object as
the resolver will give up after 2 minutes.

Reduce the value to 10 seconds to accomodate to honour the original
more closely, but still allow some leeway for clients that started some
time in the past.

Our measurements show that even setting this value to 0 has no
statistically significant effect, thus the value of 10 seconds should be
on the safe side.

lib/dns/db_p.h

@@ -32,7 +32,6 @@
 #define NODE_LOCK(l, t, tp)                                      \
 	{                                                        \
 		STRONG_RWLOCK_CHECK(*tp == isc_rwlocktype_none); \
-		rcu_read_lock();                                 \
 		RWLOCK((l), (t));                                \
 		*tp = t;                                         \
 	}
@@ -40,7 +39,6 @@
 	{                                                        \
 		STRONG_RWLOCK_CHECK(*tp != isc_rwlocktype_none); \
 		RWUNLOCK(l, *tp);                                \
-		rcu_read_unlock();                               \
 		*tp = isc_rwlocktype_none;                       \
 	}
 #define NODE_RDLOCK(l, tp) NODE_LOCK(l, isc_rwlocktype_read, tp);
@@ -48,13 +46,10 @@
 #define NODE_TRYLOCK(l, t, tp)                                   \
 	({                                                       \
 		STRONG_RWLOCK_CHECK(*tp == isc_rwlocktype_none); \
-		rcu_read_lock();                                 \
 		isc_result_t _result = isc_rwlock_trylock(l, t); \
 		if (_result == ISC_R_SUCCESS) {                  \
 			*tp = t;                                 \
-		} else {                                         \
-			rcu_read_unlock();                       \
-		}                                                \
+		};                                               \
 		_result;                                         \
 	})
 #define NODE_TRYRDLOCK(l, tp) NODE_TRYLOCK(l, isc_rwlocktype_read, tp)

lib/dns/include/dns/rdataslab.h

@@ -43,8 +43,6 @@
 
 #include <stdbool.h>
 
-#include <urcu/rculfhash.h>
-
 #include <isc/atomic.h>
 #include <isc/heap.h>
 #include <isc/stdtime.h>
@@ -105,31 +103,22 @@ struct dns_slabheader {
 	 */
 
 	union {
-		struct {
-			struct cds_lfht_node ht_node;
-			struct rcu_head	     rcu_head;
-		};
-		struct {
-			union {
-				struct dns_slabheader *next;
-				struct dns_slabheader *up;
-			};
-			/*%<
-			 * If this is the top header for an rdataset, 'next'
-			 * points to the top header for the next rdataset (i.e.,
-			 * the next type).
-			 *
-			 * Otherwise 'up' points up to the header whose down
-			 * pointer points at this header.
-			 */
-
-			struct dns_slabheader *down;
-			/*%<
-			 * Points to the header for the next older version of
-			 * this rdataset.
-			 */
-		};
+		struct dns_slabheader *next;
+		struct dns_slabheader *up;
 	};
+	/*%<
+	 * If this is the top header for an rdataset, 'next' points
+	 * to the top header for the next rdataset (i.e., the next type).
+	 *
+	 * Otherwise 'up' points up to the header whose down pointer points at
+	 * this header.
+	 */
+
+	struct dns_slabheader *down;
+	/*%<
+	 * Points to the header for the next older version of
+	 * this rdataset.
+	 */
 
 	dns_db_t     *db;
 	dns_dbnode_t *node;