Make the TTL-based cleaning more aggressive

It was discovered that the TTL-based cleaning could build up
a significant backlog of the rdataset headers during the periods where
the top of the TTL heap isn't expired yet.  Make the TTL-based cleaning
more aggressive by cleaning more headers from the heap when we are
adding new header into the RBTDB.

(cherry picked from commit d8220ca4ca45e0aadf1ad938ed6264c8f95c7e55)

diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index 850aae00771fc1a350ff1e22194a30e1485585f3..380218cde9a1c423463fc7335e854f7b95599b3f 100644 (file)
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -389,6 +389,14 @@ hash_32(uint32_t val, unsigned int bits) {
 #define DEFAULT_CACHE_NODE_LOCK_COUNT 17
 #endif /* DNS_RBTDB_CACHE_NODE_LOCK_COUNT */
 
+/*
+ * This defines the number of headers that we try to expire each time the
+ * expire_ttl_headers() is run.  The number should be small enough, so the
+ * TTL-based header expiration doesn't take too long, but it should be large
+ * enough, so we expire enough headers if their TTL is clustered.
+ */
+#define DNS_RBTDB_EXPIRE_TTL_COUNT 10
+
 typedef struct {
        nodelock_t lock;
        /* Protected in the refcount routines. */
@@ -6940,6 +6948,10 @@ rdataset_size(rdatasetheader_t *header) {
        return (sizeof(*header));
 }
 
+static void
+expire_ttl_headers(dns_rbtdb_t *rbtdb, unsigned int locknum, bool tree_locked,
+                  isc_stdtime_t now);
+
 static isc_result_t
 addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
            isc_stdtime_t now, dns_rdataset_t *rdataset, unsigned int options,
@@ -6949,7 +6961,6 @@ addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
        rbtdb_version_t *rbtversion = version;
        isc_region_t region;
        rdatasetheader_t *newheader;
-       rdatasetheader_t *header;
        isc_result_t result;
        bool delegating;
        bool newnsec;
@@ -7123,20 +7134,7 @@ addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
                        cleanup_dead_nodes(rbtdb, rbtnode->locknum);
                }
 
-               header = isc_heap_element(rbtdb->heaps[rbtnode->locknum], 1);
-               if (header != NULL) {
-                       dns_ttl_t rdh_ttl = header->rdh_ttl;
-
-                       /* Only account for stale TTL if cache is not overmem */
-                       if (!cache_is_overmem) {
-                               rdh_ttl += rbtdb->serve_stale_ttl;
-                       }
-
-                       if (rdh_ttl < now - RBTDB_VIRTUAL) {
-                               expire_header(rbtdb, header, tree_locked,
-                                             expire_ttl);
-                       }
-               }
+               expire_ttl_headers(rbtdb, rbtnode->locknum, tree_locked, now);
 
                /*
                 * If we've been holding a write lock on the tree just for
@@ -10778,3 +10776,40 @@ expire_header(dns_rbtdb_t *rbtdb, rdatasetheader_t *header, bool tree_locked,
                }
        }
 }
+
+/*
+ * Caller must be holding the node write lock.
+ */
+static void
+expire_ttl_headers(dns_rbtdb_t *rbtdb, unsigned int locknum, bool tree_locked,
+                  isc_stdtime_t now) {
+       isc_heap_t *heap = rbtdb->heaps[locknum];
+
+       for (size_t i = 0; i < DNS_RBTDB_EXPIRE_TTL_COUNT; i++) {
+               rdatasetheader_t *header = isc_heap_element(heap, 1);
+
+               if (header == NULL) {
+                       /* No headers left on this TTL heap; exit cleaning */
+                       return;
+               }
+
+               dns_ttl_t ttl = header->rdh_ttl;
+
+               if (!isc_mem_isovermem(rbtdb->common.mctx)) {
+                       /* Only account for stale TTL if cache is not overmem */
+                       ttl += rbtdb->serve_stale_ttl;
+               }
+
+               if (ttl >= now - RBTDB_VIRTUAL) {
+                       /*
+                        * The header at the top of this TTL heap is not yet
+                        * eligible for expiry, so none of the other headers on
+                        * the same heap can be eligible for expiry, either;
+                        * exit cleaning.
+                        */
+                       return;
+               }
+
+               expire_header(rbtdb, header, tree_locked, expire_ttl);
+       }
+}