restartable cache

"-e /path/to/tmpfsmnt/file"
SIGUSR1 for graceful stop

restart requires the same memory limit, slab sizes, and some other
infrequently changed details. Most other options and features can
change between restarts. Binary can be upgraded between restarts.

Restart does some fixup work on start for every item in cache. Can take
over a minute with more than a few hundred million items in cache.

Keep in mind when a cache is down it may be missing invalidations,
updates, and so on.

1 files changed, 33 insertions, 2 deletions

diff --git a/items.c b/items.c
index 1a7c42a..aa77f15 100644
--- a/items.c
+++ b/items.c
@@ -60,6 +60,7 @@ static uint64_t sizes_bytes[LARGEST_ID];
 static unsigned int *stats_sizes_hist = NULL;
 static uint64_t stats_sizes_cas_min = 0;
 static int stats_sizes_buckets = 0;
+static uint64_t cas_id = 0;
 
 static volatile int do_run_lru_maintainer_thread = 0;
 static int lru_maintainer_initialized = 0;
@@ -109,13 +110,18 @@ static uint64_t lru_total_bumps_dropped(void);
 /* Get the next CAS id for a new item. */
 /* TODO: refactor some atomics for this. */
 uint64_t get_cas_id(void) {
-    static uint64_t cas_id = 0;
     pthread_mutex_lock(&cas_id_lock);
     uint64_t next_id = ++cas_id;
     pthread_mutex_unlock(&cas_id_lock);
     return next_id;
 }
 
+void set_cas_id(uint64_t new_cas) {
+    pthread_mutex_lock(&cas_id_lock);
+    cas_id = new_cas;
+    pthread_mutex_unlock(&cas_id_lock);
+}
+
 int item_is_flushed(item *it) {
     rel_time_t oldest_live = settings.oldest_live;
     uint64_t cas = ITEM_get_cas(it);
@@ -293,7 +299,7 @@ item *do_item_alloc(char *key, const size_t nkey, const unsigned int flags,
         return NULL;
     }
 
-    assert(it->slabs_clsid == 0);
+    assert(it->it_flags == 0 || it->it_flags == ITEM_CHUNKED);
     //assert(it != heads[id]);
 
     /* Refcount is seeded to 1 by slabs_alloc() */
@@ -373,6 +379,31 @@ bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
     return slabs_clsid(ntotal) != 0;
 }
 
+/* fixing stats/references during warm start */
+void do_item_link_fixup(item *it) {
+    item **head, **tail;
+    int ntotal = ITEM_ntotal(it);
+    uint32_t hv = hash(ITEM_key(it), it->nkey);
+    assoc_insert(it, hv);
+
+    head = &heads[it->slabs_clsid];
+    tail = &tails[it->slabs_clsid];
+    if (it->prev == 0 && *head == 0) *head = it;
+    if (it->next == 0 && *tail == 0) *tail = it;
+    sizes[it->slabs_clsid]++;
+    sizes_bytes[it->slabs_clsid] += ntotal;
+
+    STATS_LOCK();
+    stats_state.curr_bytes += ntotal;
+    stats_state.curr_items += 1;
+    stats.total_items += 1;
+    STATS_UNLOCK();
+
+    item_stats_sizes_add(it);
+
+    return;
+}
+
 static void do_item_link_q(item *it) { /* item is the new head */
     item **head, **tail;
     assert((it->it_flags & ITEM_SLABBED) == 0);