Add new stats expired_unfetched, evicted_unfetched

The two stats represent items which expired and memory was reused, and valid
items which were evicted, but never touched by get/incr/append/etc
operations in the meantime.

Useful for seeing how many wasted items are being set and then rolling out
through the bottom of the LRU's.

doc/protocol.txt

@@ -449,7 +449,12 @@ integers separated by a colon (treat this as a floating point number).
 | 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
+|                       |         | grown to a new size                       |
+| expired_unfetched     | 64u     | Items pulled from LRU that were never     |
+|                       |         | touched by get/incr/append/etc before     |
+|                       |         | expiring                                  |
+| evicted_unfetched     | 64u     | Items evicted from LRU that were never    |
+|                       |         | touched by get/incr/append/etc.           |
 |-----------------------+---------+-------------------------------------------|
 
 Settings statistics
@@ -531,6 +536,10 @@ tailrepairs            Number of times we self-healed a slab with a refcount
                        report your situation to the developers.
 reclaimed              Number of times an entry was stored using memory from
                        an expired entry.
+expired_unfetched      Number of expired items reclaimed from the LRU which
+                       were never touched after being set.
+evicted_unfetched      Number of valid items evicted from the LRU which were
+                       never touched after being set.
 
 Note this will only display information about slabs which exist, so an empty
 cache will return an empty set.

items.c

@@ -32,6 +32,8 @@ typedef struct {
     unsigned int reclaimed;
     unsigned int outofmemory;
     unsigned int tailrepairs;
+    unsigned int expired_unfetched;
+    unsigned int evicted_unfetched;
 } itemstats_t;
 
 static item *heads[LARGEST_ID];
@@ -115,6 +117,12 @@ item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_tim
             stats.reclaimed++;
             STATS_UNLOCK();
             itemstats[id].reclaimed++;
+            if ((it->it_flags & ITEM_FETCHED) == 0) {
+                STATS_LOCK();
+                stats.expired_unfetched++;
+                STATS_UNLOCK();
+                itemstats[id].expired_unfetched++;
+            }
             it->refcount = 1;
             slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);
             do_item_unlink(it);
@@ -160,6 +168,12 @@ item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_tim
                     itemstats[id].evicted_time = current_time - search->time;
                     if (search->exptime != 0)
                         itemstats[id].evicted_nonzero++;
+                    if ((search->it_flags & ITEM_FETCHED) == 0) {
+                        STATS_LOCK();
+                        stats.evicted_unfetched++;
+                        STATS_UNLOCK();
+                        itemstats[id].evicted_unfetched++;
+                    }
                     STATS_LOCK();
                     stats.evictions++;
                     STATS_UNLOCK();
@@ -168,6 +182,12 @@ item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_tim
                     STATS_LOCK();
                     stats.reclaimed++;
                     STATS_UNLOCK();
+                    if ((search->it_flags & ITEM_FETCHED) == 0) {
+                        STATS_LOCK();
+                        stats.expired_unfetched++;
+                        STATS_UNLOCK();
+                        itemstats[id].expired_unfetched++;
+                    }
                 }
                 do_item_unlink(search);
                 break;
@@ -439,9 +459,13 @@ void do_item_stats(ADD_STAT add_stats, void *c) {
             APPEND_NUM_FMT_STAT(fmt, i, "outofmemory",
                                 "%u", itemstats[i].outofmemory);
             APPEND_NUM_FMT_STAT(fmt, i, "tailrepairs",
-                                "%u", itemstats[i].tailrepairs);;
+                                "%u", itemstats[i].tailrepairs);
             APPEND_NUM_FMT_STAT(fmt, i, "reclaimed",
-                                "%u", itemstats[i].reclaimed);;
+                                "%u", itemstats[i].reclaimed);
+            APPEND_NUM_FMT_STAT(fmt, i, "expired_unfetched",
+                                "%u", itemstats[i].expired_unfetched);
+            APPEND_NUM_FMT_STAT(fmt, i, "evicted_unfetched",
+                                "%u", itemstats[i].evicted_unfetched);
         }
     }
 
@@ -522,6 +546,7 @@ item *do_item_get(const char *key, const size_t nkey) {
 
     if (it != NULL) {
         it->refcount++;
+        it->it_flags |= ITEM_FETCHED;
         DEBUG_REFCNT(it, '+');
     }
 

memcached.c

@@ -169,6 +169,7 @@ static void stats_init(void) {
     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.expired_unfetched = stats.evicted_unfetched = 0;
     stats.accepting_conns = true; /* assuming we start in this state. */
 
     /* make the time we started always be 2 seconds before we really
@@ -2561,6 +2562,8 @@ static void server_stats(ADD_STAT add_stats, conn *c) {
     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);
+    APPEND_STAT("expired_unfetched", "%llu", stats.expired_unfetched);
+    APPEND_STAT("evicted_unfetched", "%llu", stats.evicted_unfetched);
     STATS_UNLOCK();
 }
 
@@ -4869,7 +4872,7 @@ int main (int argc, char **argv) {
                     fprintf(stderr, "Initial hashtable multiplier of %d is too high\n"
                         "Choose a value based on \"STAT hash_power_level\" from a running instance\n",
                         settings.hashpower_init);
-                    return 1; 
+                    return 1;
                 }
                 break;
             default:

memcached.h

@@ -263,6 +263,8 @@ struct stats {
     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 */
+    uint64_t      expired_unfetched; /* items reclaimed but never touched */
+    uint64_t      evicted_unfetched; /* items evicted but never touched */
 };
 
 #define MAX_VERBOSITY_LEVEL 2
@@ -309,6 +311,8 @@ extern struct settings settings;
 /* temp */
 #define ITEM_SLABBED 4
 
+#define ITEM_FETCHED 8
+
 /**
  * Structure for storing items within memcached.
  */

t/binary.t

@@ -2,7 +2,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 3470;
+use Test::More tests => 3533;
 use FindBin qw($Bin);
 use lib "$Bin/lib";
 use MemcachedTest;

t/stats.t

@@ -58,7 +58,7 @@ my $sock = $server->sock;
 my $stats = mem_stats($sock);
 
 # Test number of keys
-is(scalar(keys(%$stats)), 43, "43 stats values");
+is(scalar(keys(%$stats)), 48, "48 stats values");
 
 # Test initial state
 foreach my $key (qw(curr_items total_items bytes cmd_get cmd_set get_hits evictions get_misses