diff --git a/CHANGES b/CHANGES
index 95947c0ca9..062279936e 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+3053.	[bug]		Under a sustained high query load with a finite
+			max-cache-size, it was possible for cache memory
+			to be exhausted and not recovered. [RT #23371]
+
 3052.	[test]		Fixed last autosign test report. [RT #23256]
 
 3051.	[bug]		NS records obsure DS records at the bottom of the
diff --git a/bin/named/server.c b/bin/named/server.c
index d5e2445964..dac5755583 100644
--- a/bin/named/server.c
+++ b/bin/named/server.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: server.c,v 1.604 2011/02/23 03:08:09 marka Exp $ */
+/* $Id: server.c,v 1.605 2011/03/03 04:42:25 each Exp $ */
 
 /*! \file */
 
@@ -1587,7 +1587,7 @@ configure_view(dns_view_t *view, cfg_parser_t* parser,
 	isc_uint32_t lame_ttl;
 	dns_tsig_keyring_t *ring = NULL;
 	dns_view_t *pview = NULL;	/* Production view */
-	isc_mem_t *cmctx;
+	isc_mem_t *cmctx = NULL, *hmctx = NULL;
 	dns_dispatch_t *dispatch4 = NULL;
 	dns_dispatch_t *dispatch6 = NULL;
 	isc_boolean_t reused_cache = ISC_FALSE;
@@ -1619,8 +1619,6 @@ configure_view(dns_view_t *view, cfg_parser_t* parser,
 
 	REQUIRE(DNS_VIEW_VALID(view));
 
-	cmctx = NULL;
-
 	if (config != NULL)
 		(void)cfg_map_get(config, "options", &options);
 
@@ -2103,13 +2101,21 @@ configure_view(dns_view_t *view, cfg_parser_t* parser,
 			 * view but is not yet configured.  If it is not the
 			 * view name but not a forward reference either, then it
 			 * is simply a named cache that is not shared.
+			 *
+			 * We use two separate memory contexts for the
+			 * cache, for the main cache memory and the heap
+			 * memory.
 			 */
 			CHECK(isc_mem_create(0, 0, &cmctx));
 			isc_mem_setname(cmctx, "cache", NULL);
-			CHECK(dns_cache_create2(cmctx, ns_g_taskmgr,
+			CHECK(isc_mem_create(0, 0, &hmctx));
+			isc_mem_setname(hmctx, "cache_heap", NULL);
+			CHECK(dns_cache_create3(cmctx, hmctx, ns_g_taskmgr,
 						ns_g_timermgr, view->rdclass,
 						cachename, "rbt", 0, NULL,
 						&cache));
+			isc_mem_detach(&cmctx);
+			isc_mem_detach(&hmctx);
 		}
 		nsc = isc_mem_get(mctx, sizeof(*nsc));
 		if (nsc == NULL) {
@@ -2947,6 +2953,8 @@ configure_view(dns_view_t *view, cfg_parser_t* parser,
 		dns_order_detach(&order);
 	if (cmctx != NULL)
 		isc_mem_detach(&cmctx);
+	if (hmctx != NULL)
+		isc_mem_detach(&hmctx);
 
 	if (cache != NULL)
 		dns_cache_detach(&cache);
diff --git a/lib/dns/cache.c b/lib/dns/cache.c
index 6c971441b9..b230f5d600 100644
--- a/lib/dns/cache.c
+++ b/lib/dns/cache.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: cache.c,v 1.87 2009/11/12 23:43:02 each Exp $ */
+/* $Id: cache.c,v 1.88 2011/03/03 04:42:25 each Exp $ */
 
 /*! \file */
 
@@ -40,6 +40,8 @@
 #include <dns/rdatasetiter.h>
 #include <dns/result.h>
 
+#include "rbtdb.h"
+
 #define CACHE_MAGIC		ISC_MAGIC('$', '$', '$', '$')
 #define VALID_CACHE(cache)	ISC_MAGIC_VALID(cache, CACHE_MAGIC)
 
@@ -121,7 +123,8 @@ struct dns_cache {
 	unsigned int		magic;
 	isc_mutex_t		lock;
 	isc_mutex_t		filelock;
-	isc_mem_t		*mctx;
+	isc_mem_t		*mctx;		/* Main cache memory */
+	isc_mem_t		*hmctx;		/* Heap memory */
 	char			*name;
 
 	/* Locked by 'lock'. */
@@ -168,41 +171,54 @@ cache_create_db(dns_cache_t *cache, dns_db_t **db) {
 }
 
 isc_result_t
-dns_cache_create(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
+dns_cache_create(isc_mem_t *cmctx, isc_taskmgr_t *taskmgr,
 		 isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
 		 const char *db_type, unsigned int db_argc, char **db_argv,
 		 dns_cache_t **cachep)
 {
-	return (dns_cache_create2(mctx, taskmgr, timermgr, rdclass, "",
+	return (dns_cache_create3(cmctx, cmctx, taskmgr, timermgr, rdclass, "",
 				  db_type, db_argc, db_argv, cachep));
 }
 
 isc_result_t
-dns_cache_create2(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
+dns_cache_create2(isc_mem_t *cmctx, isc_taskmgr_t *taskmgr,
+		  isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
+		  const char *cachename, const char *db_type,
+		  unsigned int db_argc, char **db_argv, dns_cache_t **cachep)
+{
+	return (dns_cache_create3(cmctx, cmctx, taskmgr, timermgr, rdclass,
+				  cachename, db_type, db_argc, db_argv,
+				  cachep));
+}
+
+isc_result_t
+dns_cache_create3(isc_mem_t *cmctx, isc_mem_t *hmctx, isc_taskmgr_t *taskmgr,
 		  isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
 		  const char *cachename, const char *db_type,
 		  unsigned int db_argc, char **db_argv, dns_cache_t **cachep)
 {
 	isc_result_t result;
 	dns_cache_t *cache;
-	int i;
+	int i, extra = 0;
 	isc_task_t *dbtask;
 
 	REQUIRE(cachep != NULL);
 	REQUIRE(*cachep == NULL);
-	REQUIRE(mctx != NULL);
+	REQUIRE(cmctx != NULL);
+	REQUIRE(hmctx != NULL);
 	REQUIRE(cachename != NULL);
 
-	cache = isc_mem_get(mctx, sizeof(*cache));
+	cache = isc_mem_get(cmctx, sizeof(*cache));
 	if (cache == NULL)
 		return (ISC_R_NOMEMORY);
 
-	cache->mctx = NULL;
-	isc_mem_attach(mctx, &cache->mctx);
+	cache->mctx = cache->hmctx = NULL;
+	isc_mem_attach(cmctx, &cache->mctx);
+	isc_mem_attach(hmctx, &cache->hmctx);
 
 	cache->name = NULL;
 	if (cachename != NULL) {
-		cache->name = isc_mem_strdup(mctx, cachename);
+		cache->name = isc_mem_strdup(cmctx, cachename);
 		if (cache->name == NULL) {
 			result = ISC_R_NOMEMORY;
 			goto cleanup_mem;
@@ -221,26 +237,38 @@ dns_cache_create2(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
 	cache->live_tasks = 0;
 	cache->rdclass = rdclass;
 
-	cache->db_type = isc_mem_strdup(mctx, db_type);
+	cache->db_type = isc_mem_strdup(cmctx, db_type);
 	if (cache->db_type == NULL) {
 		result = ISC_R_NOMEMORY;
 		goto cleanup_filelock;
 	}
 
-	cache->db_argc = db_argc;
-	if (cache->db_argc == 0)
-		cache->db_argv = NULL;
-	else {
-		cache->db_argv = isc_mem_get(mctx,
+	/*
+	 * For databases of type "rbt" we pass hmctx to dns_db_create()
+	 * via cache->db_argv, followed by the rest of the arguments in
+	 * db_argv (of which there really shouldn't be any).
+	 */
+	if (strcmp(cache->db_type, "rbt") == 0)
+		extra = 1;
+
+	cache->db_argc = db_argc + extra;
+	cache->db_argv = NULL;
+
+	if (cache->db_argc != 0) {
+		cache->db_argv = isc_mem_get(cmctx,
 					     cache->db_argc * sizeof(char *));
 		if (cache->db_argv == NULL) {
 			result = ISC_R_NOMEMORY;
 			goto cleanup_dbtype;
 		}
+
 		for (i = 0; i < cache->db_argc; i++)
 			cache->db_argv[i] = NULL;
-		for (i = 0; i < cache->db_argc; i++) {
-			cache->db_argv[i] = isc_mem_strdup(mctx, db_argv[i]);
+
+		cache->db_argv[0] = (char *) hmctx;
+		for (i = extra; i < cache->db_argc; i++) {
+			cache->db_argv[i] = isc_mem_strdup(cmctx,
+							   db_argv[i - extra]);
 			if (cache->db_argv[i] == NULL) {
 				result = ISC_R_NOMEMORY;
 				goto cleanup_dbargv;
@@ -248,6 +276,9 @@ dns_cache_create2(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
 		}
 	}
 
+	/*
+	 * Create the database
+	 */
 	cache->db = NULL;
 	result = cache_create_db(cache, &cache->db);
 	if (result != ISC_R_SUCCESS)
@@ -284,29 +315,28 @@ dns_cache_create2(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
  cleanup_db:
 	dns_db_detach(&cache->db);
  cleanup_dbargv:
-	for (i = 0; i < cache->db_argc; i++)
+	for (i = extra; i < cache->db_argc; i++)
 		if (cache->db_argv[i] != NULL)
-			isc_mem_free(mctx, cache->db_argv[i]);
+			isc_mem_free(cmctx, cache->db_argv[i]);
 	if (cache->db_argv != NULL)
-		isc_mem_put(mctx, cache->db_argv,
+		isc_mem_put(cmctx, cache->db_argv,
 			    cache->db_argc * sizeof(char *));
  cleanup_dbtype:
-	isc_mem_free(mctx, cache->db_type);
+	isc_mem_free(cmctx, cache->db_type);
  cleanup_filelock:
 	DESTROYLOCK(&cache->filelock);
  cleanup_lock:
 	DESTROYLOCK(&cache->lock);
  cleanup_mem:
 	if (cache->name != NULL)
-		isc_mem_free(mctx, cache->name);
-	isc_mem_put(mctx, cache, sizeof(*cache));
-	isc_mem_detach(&mctx);
+		isc_mem_free(cmctx, cache->name);
+	isc_mem_detach(&cache->hmctx);
+	isc_mem_putanddetach(&cache->mctx, cache, sizeof(*cache));
 	return (result);
 }
 
 static void
 cache_free(dns_cache_t *cache) {
-	isc_mem_t *mctx;
 	int i;
 
 	REQUIRE(VALID_CACHE(cache));
@@ -337,7 +367,14 @@ cache_free(dns_cache_t *cache) {
 		dns_db_detach(&cache->db);
 
 	if (cache->db_argv != NULL) {
-		for (i = 0; i < cache->db_argc; i++)
+		/*
+		 * We don't free db_argv[0] in "rbt" cache databases
+		 * as it's a pointer to hmctx
+		 */
+		int extra = 0;
+		if (strcmp(cache->db_type, "rbt") == 0)
+			extra = 1;
+		for (i = extra; i < cache->db_argc; i++)
 			if (cache->db_argv[i] != NULL)
 				isc_mem_free(cache->mctx, cache->db_argv[i]);
 		isc_mem_put(cache->mctx, cache->db_argv,
@@ -352,10 +389,10 @@ cache_free(dns_cache_t *cache) {
 
 	DESTROYLOCK(&cache->lock);
 	DESTROYLOCK(&cache->filelock);
+
 	cache->magic = 0;
-	mctx = cache->mctx;
-	isc_mem_put(cache->mctx, cache, sizeof(*cache));
-	isc_mem_detach(&mctx);
+	isc_mem_detach(&cache->hmctx);
+	isc_mem_putanddetach(&cache->mctx, cache, sizeof(*cache));
 }
 
 
diff --git a/lib/dns/include/dns/cache.h b/lib/dns/include/dns/cache.h
index 1a59ea9ef2..eec4472288 100644
--- a/lib/dns/include/dns/cache.h
+++ b/lib/dns/include/dns/cache.h
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: cache.h,v 1.28 2009/01/09 23:47:46 tbox Exp $ */
+/* $Id: cache.h,v 1.29 2011/03/03 04:42:25 each Exp $ */
 
 #ifndef DNS_CACHE_H
 #define DNS_CACHE_H 1
@@ -61,23 +61,36 @@ ISC_LANG_BEGINDECLS
  ***/
 
 isc_result_t
-dns_cache_create(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
+dns_cache_create(isc_mem_t *cmctx, isc_taskmgr_t *taskmgr,
 		 isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
 		 const char *db_type, unsigned int db_argc, char **db_argv,
 		 dns_cache_t **cachep);
 isc_result_t
-dns_cache_create2(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
+dns_cache_create2(isc_mem_t *cmctx, isc_taskmgr_t *taskmgr,
+		  isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
+		  const char *cachename, const char *db_type,
+		  unsigned int db_argc, char **db_argv, dns_cache_t **cachep);
+isc_result_t
+dns_cache_create3(isc_mem_t *cmctx, isc_mem_t *hmctx, isc_taskmgr_t *taskmgr,
 		  isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
 		  const char *cachename, const char *db_type,
 		  unsigned int db_argc, char **db_argv, dns_cache_t **cachep);
 /*%<
- * Create a new DNS cache.  dns_cache_create2() will create a named cache.
- * dns_cache_create() is a backward compatible version that internally specifies
- * an empty name.
+ * Create a new DNS cache.
+ *
+ * dns_cache_create2() will create a named cache.
+ *
+ * dns_cache_create3() will create a named cache using two separate memory
+ * contexts, one for cache data which can be cleaned and a separate one for
+ * memory allocated for the heap (which can grow without an upper limit and
+ * has no mechanism for shrinking).
+ *
+ * dns_cache_create() is a backward compatible version that internally
+ * specifies an empty cache name and a single memory context.
  *
  * Requires:
  *
- *\li	'mctx' is a valid memory context
+ *\li	'cmctx' (and 'hmctx' if applicable) is a valid memory context.
  *
  *\li	'taskmgr' is a valid task manager and 'timermgr' is a valid timer
  * 	manager, or both are NULL.  If NULL, no periodic cleaning of the
diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index cd149c170f..c3fe019714 100644
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: rbtdb.c,v 1.312 2011/03/02 04:20:34 marka Exp $ */
+/* $Id: rbtdb.c,v 1.313 2011/03/03 04:42:25 each Exp $ */
 
 /*! \file */
 
@@ -433,8 +433,12 @@ typedef struct {
 	rbtnodelist_t                   *deadnodes;
 
 	/*
-	 * Heaps.  Each of these is used for TTL based expiry.
+	 * Heaps.  These are used for TTL based expiry in a cache,
+	 * or for zone resigning in a zone DB.  hmctx is the memory
+	 * context to use for the heap (which differs from the main
+	 * database memory context in the case of a cache).
 	 */
+	isc_mem_t *			hmctx;
 	isc_heap_t                      **heaps;
 
 	/* Locked by tree_lock. */
@@ -950,9 +954,8 @@ free_rbtdb(dns_rbtdb_t *rbtdb, isc_boolean_t log, isc_event_t *event) {
 	if (rbtdb->heaps != NULL) {
 		for (i = 0; i < rbtdb->node_lock_count; i++)
 			isc_heap_destroy(&rbtdb->heaps[i]);
-		isc_mem_put(rbtdb->common.mctx, rbtdb->heaps,
-			    rbtdb->node_lock_count *
-			    sizeof(isc_heap_t *));
+		isc_mem_put(rbtdb->hmctx, rbtdb->heaps,
+			    rbtdb->node_lock_count * sizeof(isc_heap_t *));
 	}
 
 	if (rbtdb->rrsetstats != NULL)
@@ -974,6 +977,7 @@ free_rbtdb(dns_rbtdb_t *rbtdb, isc_boolean_t log, isc_event_t *event) {
 	rbtdb->common.magic = 0;
 	rbtdb->common.impmagic = 0;
 	ondest = rbtdb->common.ondest;
+	isc_mem_detach(&rbtdb->hmctx);
 	isc_mem_putanddetach(&rbtdb->common.mctx, rbtdb, sizeof(*rbtdb));
 	isc_ondestroy_notify(&ondest, rbtdb);
 }
@@ -7459,16 +7463,21 @@ dns_rbtdb_create
 	int i;
 	dns_name_t name;
 	isc_boolean_t (*sooner)(void *, void *);
+	isc_mem_t *hmctx = mctx;
 
 	/* Keep the compiler happy. */
-	UNUSED(argc);
-	UNUSED(argv);
 	UNUSED(driverarg);
 
 	rbtdb = isc_mem_get(mctx, sizeof(*rbtdb));
 	if (rbtdb == NULL)
 		return (ISC_R_NOMEMORY);
 
+	/*
+	 * If argv[0] exists, it points to a memory context to use for heap
+	 */
+	if (argc != 0)
+		hmctx = (isc_mem_t *) argv[0];
+
 	memset(rbtdb, '\0', sizeof(*rbtdb));
 	dns_name_init(&rbtdb->common.origin, NULL);
 	rbtdb->common.attributes = 0;
@@ -7533,7 +7542,7 @@ dns_rbtdb_create
 	/*
 	 * Create the heaps.
 	 */
-	rbtdb->heaps = isc_mem_get(mctx, rbtdb->node_lock_count *
+	rbtdb->heaps = isc_mem_get(hmctx, rbtdb->node_lock_count *
 				   sizeof(isc_heap_t *));
 	if (rbtdb->heaps == NULL) {
 		result = ISC_R_NOMEMORY;
@@ -7543,7 +7552,7 @@ dns_rbtdb_create
 		rbtdb->heaps[i] = NULL;
 	sooner = IS_CACHE(rbtdb) ? ttl_sooner : resign_sooner;
 	for (i = 0; i < (int)rbtdb->node_lock_count; i++) {
-		result = isc_heap_create(mctx, sooner, set_index, 0,
+		result = isc_heap_create(hmctx, sooner, set_index, 0,
 					 &rbtdb->heaps[i]);
 		if (result != ISC_R_SUCCESS)
 			goto cleanup_heaps;
@@ -7587,6 +7596,7 @@ dns_rbtdb_create
 	 * mctx won't disappear out from under us.
 	 */
 	isc_mem_attach(mctx, &rbtdb->common.mctx);
+	isc_mem_attach(hmctx, &rbtdb->hmctx);
 
 	/*
 	 * Must be initialized before free_rbtdb() is called.
diff --git a/lib/dns/rbtdb.h b/lib/dns/rbtdb.h
index b024d136e8..ee9fb7d261 100644
--- a/lib/dns/rbtdb.h
+++ b/lib/dns/rbtdb.h
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: rbtdb.h,v 1.18 2007/06/19 23:47:16 tbox Exp $ */
+/* $Id: rbtdb.h,v 1.19 2011/03/03 04:42:25 each Exp $ */
 
 #ifndef DNS_RBTDB_H
 #define DNS_RBTDB_H 1
@@ -39,6 +39,19 @@ dns_rbtdb_create(isc_mem_t *mctx, dns_name_t *base, dns_dbtype_t type,
 		 dns_rdataclass_t rdclass, unsigned int argc, char *argv[],
 		 void *driverarg, dns_db_t **dbp);
 
+/*%<
+ * Create a new database of type "rbt" (or "rbt64").  Called via
+ * dns_db_create(); see documentation for that function for more details.
+ *
+ * If argv[0] is set, it points to a valid memory context to be used for
+ * allocation of heap memory.  Generally this is used for cache databases
+ * only.
+ *
+ * Requires:
+ *
+ * \li argc == 0 or argv[0] is a valid memory context.
+ */
+
 ISC_LANG_ENDDECLS
 
 #endif /* DNS_RBTDB_H */
diff --git a/lib/isc/heap.c b/lib/isc/heap.c
index 7efbd1a5e7..a976ce0f9b 100644
--- a/lib/isc/heap.c
+++ b/lib/isc/heap.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: heap.c,v 1.39 2010/02/04 23:49:13 tbox Exp $ */
+/* $Id: heap.c,v 1.40 2011/03/03 04:42:25 each Exp $ */
 
 /*! \file
  * Heap implementation of priority queues adapted from the following:
@@ -86,8 +86,9 @@ isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare,
 	if (heap == NULL)
 		return (ISC_R_NOMEMORY);
 	heap->magic = HEAP_MAGIC;
-	heap->mctx = mctx;
 	heap->size = 0;
+	heap->mctx = NULL;
+	isc_mem_attach(mctx, &heap->mctx);
 	if (size_increment == 0)
 		heap->size_increment = SIZE_INCREMENT;
 	else
@@ -114,7 +115,7 @@ isc_heap_destroy(isc_heap_t **heapp) {
 		isc_mem_put(heap->mctx, heap->array,
 			    heap->size * sizeof(void *));
 	heap->magic = 0;
-	isc_mem_put(heap->mctx, heap, sizeof(*heap));
+	isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));
 
 	*heapp = NULL;
 }