expose stats for the internal hash table

Now users can tell how much memory is being used for the hash table structure.
It also exposes the current hash power level, which is useful for presizing
the structure.

assoc.c

@@ -64,6 +64,10 @@ void assoc_init(void) {
         fprintf(stderr, "Failed to init hashtable.\n");
         exit(EXIT_FAILURE);
     }
+    STATS_LOCK();
+    stats.hash_power_level = hashpower;
+    stats.hash_bytes = hashsize(hashpower) * sizeof(void *);
+    STATS_UNLOCK();
 }
 
 item *assoc_find(const char *key, const size_t nkey) {
@@ -126,6 +130,11 @@ static void assoc_expand(void) {
         hashpower++;
         expanding = true;
         expand_bucket = 0;
+        STATS_LOCK();
+        stats.hash_power_level = hashpower;
+        stats.hash_bytes += hashsize(hashpower) * sizeof(void *);
+        stats.hash_is_expanding = 1;
+        STATS_UNLOCK();
         pthread_cond_signal(&maintenance_cond);
     } else {
         primary_hashtable = old_hashtable;
@@ -213,6 +222,10 @@ static void *assoc_maintenance_thread(void *arg) {
             if (expand_bucket == hashsize(hashpower - 1)) {
                 expanding = false;
                 free(old_hashtable);
+                STATS_LOCK();
+                stats.hash_bytes -= hashsize(hashpower - 1) * sizeof(void *);
+                stats.hash_is_expanding = 0;
+                STATS_UNLOCK();
                 if (settings.verbose > 1)
                     fprintf(stderr, "Hash table expansion done\n");
             }

doc/protocol.txt

@@ -446,6 +446,10 @@ integers separated by a colon (treat this as a floating point number).
 |                       |         | (see doc/threads.txt)                     |
 | conn_yields           | 64u     | Number of times any connection yielded to |
 |                       |         | another due to hitting the -R limit.      |
+| hash_power_level      | 32u     | Current size multiplier for hash table    |
+| hash_bytes            | 64u     | Bytes currently used by hash tables       |
+| hash_is_expanding     | bool    | Indicates if the hash table is being      |
+|                       |         | grown to a new size
 |-----------------------+---------+-------------------------------------------|
 
 Settings statistics

memcached.c

@@ -168,6 +168,7 @@ static void stats_init(void) {
     stats.get_cmds = stats.set_cmds = stats.get_hits = stats.get_misses = stats.evictions = stats.reclaimed = 0;
     stats.touch_cmds = stats.touch_misses = stats.touch_hits = stats.rejected_conns = 0;
     stats.curr_bytes = stats.listen_disabled_num = 0;
+    stats.hash_power_level = stats.hash_bytes = stats.hash_is_expanding = 0;
     stats.accepting_conns = true; /* assuming we start in this state. */
 
     /* make the time we started always be 2 seconds before we really
@@ -2556,6 +2557,9 @@ static void server_stats(ADD_STAT add_stats, conn *c) {
     APPEND_STAT("listen_disabled_num", "%llu", (unsigned long long)stats.listen_disabled_num);
     APPEND_STAT("threads", "%d", settings.num_threads);
     APPEND_STAT("conn_yields", "%llu", (unsigned long long)thread_stats.conn_yields);
+    APPEND_STAT("hash_power_level", "%u", stats.hash_power_level);
+    APPEND_STAT("hash_bytes", "%llu", (unsigned long long)stats.hash_bytes);
+    APPEND_STAT("hash_is_expanding", "%u", stats.hash_is_expanding);
     STATS_UNLOCK();
 }
 

memcached.h

@@ -257,6 +257,9 @@ struct stats {
     time_t        started;          /* when the process was started */
     bool          accepting_conns;  /* whether we are currently accepting */
     uint64_t      listen_disabled_num;
+    unsigned int  hash_power_level; /* Better hope it's not over 9000 */
+    uint64_t      hash_bytes;       /* size used for hash tables */
+    bool          hash_is_expanding; /* If the hash table is being expanded */
 };
 
 #define MAX_VERBOSITY_LEVEL 2