Lazyfree: a first implementation of non blocking DEL.

src/Makefile

@@ -117,7 +117,7 @@ endif
 
 REDIS_SERVER_NAME=redis-server
 REDIS_SENTINEL_NAME=redis-sentinel
-REDIS_SERVER_OBJ=adlist.o quicklist.o ae.o anet.o dict.o server.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking.o util.o object.o db.o replication.o rdb.o t_string.o t_list.o t_set.o t_zset.o t_hash.o config.o aof.o pubsub.o multi.o debug.o sort.o intset.o syncio.o cluster.o crc16.o endianconv.o slowlog.o scripting.o bio.o rio.o rand.o memtest.o crc64.o bitops.o sentinel.o notify.o setproctitle.o blocked.o hyperloglog.o latency.o sparkline.o redis-check-rdb.o geo.o
+REDIS_SERVER_OBJ=adlist.o quicklist.o ae.o anet.o dict.o server.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking.o util.o object.o db.o replication.o rdb.o t_string.o t_list.o t_set.o t_zset.o t_hash.o config.o aof.o pubsub.o multi.o debug.o sort.o intset.o syncio.o cluster.o crc16.o endianconv.o slowlog.o scripting.o bio.o rio.o rand.o memtest.o crc64.o bitops.o sentinel.o notify.o setproctitle.o blocked.o hyperloglog.o latency.o sparkline.o redis-check-rdb.o geo.o lazyfree.o
 REDIS_GEOHASH_OBJ=../deps/geohash-int/geohash.o ../deps/geohash-int/geohash_helper.o
 REDIS_CLI_NAME=redis-cli
 REDIS_CLI_OBJ=anet.o adlist.o redis-cli.o zmalloc.o release.o anet.o ae.o crc64.o

src/db.c

@@ -33,10 +33,6 @@
 #include <signal.h>
 #include <ctype.h>
 
-void slotToKeyAdd(robj *key);
-void slotToKeyDel(robj *key);
-void slotToKeyFlush(void);
-
 /*-----------------------------------------------------------------------------
  * C-level DB API
  *----------------------------------------------------------------------------*/
@@ -184,7 +180,7 @@ robj *dbRandomKey(redisDb *db) {
 }
 
 /* Delete a key, value, and associated expiration entry if any, from the DB */
-int dbDelete(redisDb *db, robj *key) {
+int dbSyncDelete(redisDb *db, robj *key) {
     /* Deleting an entry from the expires dict will not free the sds of
      * the key, because it is shared with the main dictionary. */
     if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
@@ -196,6 +192,14 @@ int dbDelete(redisDb *db, robj *key) {
     }
 }
 
+/* This is a wrapper whose behavior depends on the Redis lazy free
+ * configuration. Deletes the key synchronously or asynchronously. */
+int dbDelete(redisDb *db, robj *key) {
+    int async = 1; /* TODO: Fixme making this a proper option. */
+    if (async) return dbAsyncDelete(db,key);
+    else       return dbSyncDelete(db,key);
+}
+
 /* Prepare the string object stored at 'key' to be modified destructively
  * to implement commands like SETBIT or APPEND.
  *
@@ -302,20 +306,31 @@ void flushallCommand(client *c) {
     server.dirty++;
 }
 
-void delCommand(client *c) {
-    int deleted = 0, j;
+/* This command implements DEL and LAZYDEL. */
+void delGenericCommand(client *c, int lazy) {
+    int numdel = 0, j;
 
     for (j = 1; j < c->argc; j++) {
         expireIfNeeded(c->db,c->argv[j]);
-        if (dbDelete(c->db,c->argv[j])) {
+        int deleted  = lazy ? dbAsyncDelete(c->db,c->argv[j]) :
+                              dbSyncDelete(c->db,c->argv[j]);
+        if (deleted) {
             signalModifiedKey(c->db,c->argv[j]);
             notifyKeyspaceEvent(NOTIFY_GENERIC,
                 "del",c->argv[j],c->db->id);
             server.dirty++;
-            deleted++;
+            numdel++;
         }
     }
-    addReplyLongLong(c,deleted);
+    addReplyLongLong(c,numdel);
+}
+
+void delCommand(client *c) {
+    delGenericCommand(c,0);
+}
+
+void unlinkCommand(client *c) {
+    delGenericCommand(c,1);
 }
 
 /* EXISTS key1 key2 ... key_N.

src/dict.c

@@ -855,7 +855,7 @@ unsigned long dictScan(dict *d,
                        void *privdata)
 {
     dictht *t0, *t1;
-    const dictEntry *de;
+    const dictEntry *de, *next;
     unsigned long m0, m1;
 
     if (dictSize(d) == 0) return 0;
@@ -867,8 +867,9 @@ unsigned long dictScan(dict *d,
         /* Emit entries at cursor */
         de = t0->table[v & m0];
         while (de) {
+            next = de->next;
             fn(privdata, de);
-            de = de->next;
+            de = next;
         }
 
     } else {
@@ -887,8 +888,9 @@ unsigned long dictScan(dict *d,
         /* Emit entries at cursor */
         de = t0->table[v & m0];
         while (de) {
+            next = de->next;
             fn(privdata, de);
-            de = de->next;
+            de = next;
         }
 
         /* Iterate over indices in larger table that are the expansion
@@ -897,8 +899,9 @@ unsigned long dictScan(dict *d,
             /* Emit entries at cursor */
             de = t1->table[v & m1];
             while (de) {
+                next = de->next;
                 fn(privdata, de);
-                de = de->next;
+                de = next;
             }
 
             /* Increment bits not covered by the smaller mask */

src/dict.h

@@ -78,7 +78,7 @@ typedef struct dict {
     void *privdata;
     dictht ht[2];
     long rehashidx; /* rehashing not in progress if rehashidx == -1 */
-    int iterators; /* number of iterators currently running */
+    unsigned long iterators; /* number of iterators currently running */
 } dict;
 
 /* If safe is set to 1 this is a safe iterator, that means, you can call

src/lazyfree.c

+#include "server.h"
+
+/* Initialization of the lazy free engine. Must be called only once at server
+ * startup. */
+void initLazyfreeEngine(void) {
+    server.lazyfree_dbs = listCreate();
+    server.lazyfree_obj = listCreate();
+    server.lazyfree_elements = 0;
+}
+
+/* Return the amount of work needed in order to free an object.
+ * The return value is not always the actual number of allocations the
+ * object is compoesd of, but a number proportional to it.
+ *
+ * For strings the function always returns 1.
+ *
+ * For aggregated objects represented by hash tables or other data structures
+ * the function just returns the number of elements the object is composed of.
+ *
+ * Objects composed of single allocations are always reported as having a
+ * single item even if they are actaully logical composed of multiple
+ * elements.
+ *
+ * For lists the funciton returns the number of elements in the quicklist
+ * representing the list. */
+size_t lazyfreeGetFreeEffort(robj *obj) {
+    if (obj->type == OBJ_LIST) {
+        quicklist *ql = obj->ptr;
+        return ql->len;
+    } else if (obj->type == OBJ_SET && obj->encoding == OBJ_ENCODING_HT) {
+        dict *ht = obj->ptr;
+        return dictSize(ht);
+    } else if (obj->type == OBJ_ZSET && obj->encoding == OBJ_ENCODING_SKIPLIST){
+        zset *zs = obj->ptr;
+        return zs->zsl->length;
+    } else if (obj->type == OBJ_HASH && obj->encoding == OBJ_ENCODING_HT) {
+        dict *ht = obj->ptr;
+        return dictSize(ht);
+    } else {
+        return 1; /* Everything else is a single allocation. */
+    }
+}
+
+/* This callback is used together with dictScan() in order to free a dict.c
+ * hash table incrementally. */
+void lazyfreeScanCallback(void *privdata, const dictEntry *de) {
+    dict *ht = privdata;
+    long saved_iterators = ht->iterators;
+    ht->iterators = 1; /* Make sure no rehashing happens. */
+    dictDelete(ht,dictGetKey(de));
+    ht->iterators = saved_iterators;
+}
+
+/* Free some object from the lazy free list. */
+#define LAZYFREE_ITER_PER_STEP 100
+size_t lazyfreeFastStep(void) {
+    size_t maxiter = LAZYFREE_ITER_PER_STEP;
+    size_t workdone = 0;
+    robj *current = NULL;
+
+    while(maxiter--) {
+        if (current == NULL) {
+            listNode *ln = listFirst(server.lazyfree_obj);
+            if (ln == NULL) break; /* Nothing more to free. */
+            current = ln->value;
+        }
+        if ((current->type == OBJ_SET ||
+            current->type == OBJ_HASH) &&
+            current->encoding == OBJ_ENCODING_HT)
+        {
+            dict *ht = current->ptr;
+            size_t origsize = dictSize(ht);
+            ht->iterators = dictScan(ht,ht->iterators,lazyfreeScanCallback,ht);
+            workdone++; /* We are not sure how many elements we freed, even if
+                           zero, the free list is non empty so we don't return
+                           0 to the caller. */
+            server.lazyfree_elements -= (origsize - dictSize(ht));
+            if (dictSize(ht) == 0) {
+                decrRefCount(current);
+                listNode *ln = listFirst(server.lazyfree_obj);
+                listDelNode(server.lazyfree_obj,ln);
+                current = NULL;
+            }
+        } else {
+            /* Not handled type or encoding. Do a blocking free. */
+            size_t effort = lazyfreeGetFreeEffort(current);
+            server.lazyfree_elements -= effort;
+            workdone += effort;
+            decrRefCount(current);
+            listNode *ln = listFirst(server.lazyfree_obj);
+            listDelNode(server.lazyfree_obj,ln);
+            current = NULL;
+        }
+    }
+    return workdone;
+}
+
+/* Handles slow or fast collection steps. */
+size_t lazyfreeStep(int type) {
+    if (type == LAZYFREE_STEP_FAST) return lazyfreeFastStep();
+
+    size_t totalwork = 0;
+    mstime_t end = mstime()+2;
+    do {
+        size_t workdone = lazyfreeFastStep();
+        if (workdone == 0) break;
+        totalwork += workdone;
+    } while(mstime() < end);
+    return totalwork;
+}
+
+/* Delete a key, value, and associated expiration entry if any, from the DB.
+ * If there are enough allocations to free the value object may be put into
+ * a lazy free list instead of being freed synchronously. The lazy free list
+ * will be reclaimed incrementally in a non blocking way. */
+#define LAZYFREE_THRESHOLD 64
+int dbAsyncDelete(redisDb *db, robj *key) {
+    /* Deleting an entry from the expires dict will not free the sds of
+     * the key, because it is shared with the main dictionary. */
+    if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
+
+    /* If the value is composed of a few allocations, to free in a lazy way
+     * is actually just slower... So under a certain limit we just free
+     * the object synchronously. */
+    dictEntry *de = dictFind(db->dict,key->ptr);
+    if (de) {
+        robj *val = dictGetVal(de);
+        size_t free_effort = lazyfreeGetFreeEffort(val);
+
+        /* If releasing the object is too much work, let's put it into the
+         * lazy free list. */
+        if (free_effort > LAZYFREE_THRESHOLD) {
+            listAddNodeTail(server.lazyfree_obj,val);
+            server.lazyfree_elements += free_effort;
+            dictSetVal(db->dict,de,NULL);
+        }
+    }
+
+    /* Release the key-val pair, or just the key if we set the val
+     * field to NULL in order to lazy free it later. */
+    if (dictDelete(db->dict,key->ptr) == DICT_OK) {
+        if (server.cluster_enabled) slotToKeyDel(key);
+        return 1;
+    } else {
+        return 0;
+    }
+}
+
+/* This is the timer handler we use to incrementally perform collection
+ * into the lazy free lists. We can't use serverCron since we need a
+ * very high timer frequency when there are many objects to collect, while
+ * we lower the frequency to just 1HZ when there is nothing to do.
+ *
+ * Since a slow lazy free step will take 1.5 milliseconds and we modulate
+ * the timer frequency from 1 to 333 HZ in an adaptive way, the CPU
+ * used is between 0% (nothing in the lazy free list) to 50%.
+ *
+ * The frequency is obtained as follows: if the lazy free list is empty
+ * it is set to 1HZ. If the lazy free has elements the call period starts
+ * at 20 (50HZ) and is decremented (up to 3 ms = 333HZ) each time the server
+ * used memory raises between calls of this function. */
+int lazyfreeCron(struct aeEventLoop *eventLoop, long long id, void *clientData)
+{
+    UNUSED(eventLoop);
+    UNUSED(id);
+    UNUSED(clientData);
+
+    static size_t prev_mem;
+    static int timer_period = 1000; /* Defauls to 1HZ */
+    static double mem_trend = 0;
+    size_t mem = zmalloc_used_memory();
+
+    /* Compute the memory trend, biased towards thinking memory is raising
+     * for a few calls every time previous and current memory raise. */
+    if (prev_mem < mem) mem_trend = 1;
+    mem_trend *= 0.9; /* Make it slowly forget. */
+    int mem_is_raising = mem_trend > .1;
+
+    /* Free a few items. */
+    size_t workdone = lazyfreeStep(LAZYFREE_STEP_SLOW);
+
+    /* Adjust this timer call frequency according to the current state. */
+    if (workdone) {
+        if (timer_period == 1000) timer_period = 20;
+        if (mem_is_raising && timer_period > 3)
+            timer_period--; /* Raise call frequency. */
+        else if (!mem_is_raising && timer_period < 20)
+            timer_period++; /* Lower call frequency. */
+    } else {
+        timer_period = 1000;    /* 1 HZ */
+    }
+    prev_mem = mem;
+#if 0
+    printf("%llu (%d hz) %s (%f)\n",
+        (unsigned long long)server.lazyfree_elements,
+        1000/timer_period,
+        mem_is_raising ? "RAISING" : "lowering",
+        mem_trend);
+#endif
+    return timer_period;
+}

src/object.c

@@ -48,6 +48,23 @@ robj *createObject(int type, void *ptr) {
     return o;
 }
 
+/* Set a special refcount in the object to make it "shared":
+ * incrRefCount and decrRefCount() will test for this special refcount
+ * and will not touch the object. This way it is free to access shared
+ * objects such as small integers from different threads without any
+ * mutex.
+ *
+ * A common patter to create shared objects:
+ *
+ * robj *myobject = makeObjectShared(createObject(...));
+ *
+ */
+robj *makeObjectShared(robj *o) {
+    serverAssert(o->refcount == 1);
+    o->refcount = OBJ_SHARED_REFCOUNT;
+    return o;
+}
+
 /* Create a string object with encoding OBJ_ENCODING_RAW, that is a plain
  * string object where o->ptr points to a proper sds string. */
 robj *createRawStringObject(const char *ptr, size_t len) {
@@ -295,11 +312,10 @@ void freeHashObject(robj *o) {
 }
 
 void incrRefCount(robj *o) {
-    o->refcount++;
+    if (o->refcount != OBJ_SHARED_REFCOUNT) o->refcount++;
 }
 
 void decrRefCount(robj *o) {
-    if (o->refcount <= 0) serverPanic("decrRefCount against refcount <= 0");
     if (o->refcount == 1) {
         switch(o->type) {
         case OBJ_STRING: freeStringObject(o); break;
@@ -311,7 +327,8 @@ void decrRefCount(robj *o) {
         }
         zfree(o);
     } else {
-        o->refcount--;
+        if (o->refcount <= 0) serverPanic("decrRefCount against refcount <= 0");
+        if (o->refcount != OBJ_SHARED_REFCOUNT) o->refcount--;
     }
 }
 

src/server.c

@@ -131,6 +131,7 @@ struct redisCommand redisCommandTable[] = {
     {"append",appendCommand,3,"wm",0,NULL,1,1,1,0,0},
     {"strlen",strlenCommand,2,"rF",0,NULL,1,1,1,0,0},
     {"del",delCommand,-2,"w",0,NULL,1,-1,1,0,0},
+    {"unlink",unlinkCommand,-2,"wF",0,NULL,1,-1,1,0,0},
     {"exists",existsCommand,-2,"rF",0,NULL,1,-1,1,0,0},
     {"setbit",setbitCommand,4,"wm",0,NULL,1,1,1,0,0},
     {"getbit",getbitCommand,3,"rF",0,NULL,1,1,1,0,0},
@@ -458,7 +459,7 @@ void dictObjectDestructor(void *privdata, void *val)
 {
     DICT_NOTUSED(privdata);
 
-    if (val == NULL) return; /* Values of swapped out keys as set to NULL */
+    if (val == NULL) return; /* Lazy freeing will set value to NULL. */
     decrRefCount(val);
 }
 
@@ -1286,6 +1287,11 @@ void beforeSleep(struct aeEventLoop *eventLoop) {
      * later in this function. */
     if (server.cluster_enabled) clusterBeforeSleep();
 
+    /* Lazy free a few objects before to return to the event loop, this way
+     * if there is activity in the server (that may generate writes) we
+     * reclaim memory at a faster rate. */
+    lazyfreeStep(LAZYFREE_STEP_FAST);
+
     /* Run a fast expire cycle (the called function will return
      * ASAP if a fast cycle is not needed). */
     if (server.active_expire_enabled && server.masterhost == NULL)
@@ -1397,7 +1403,8 @@ void createSharedObjects(void) {
     shared.lpop = createStringObject("LPOP",4);
     shared.lpush = createStringObject("LPUSH",5);
     for (j = 0; j < OBJ_SHARED_INTEGERS; j++) {
-        shared.integers[j] = createObject(OBJ_STRING,(void*)(long)j);
+        shared.integers[j] =
+            makeObjectShared(createObject(OBJ_STRING,(void*)(long)j));
         shared.integers[j]->encoding = OBJ_ENCODING_INT;
     }
     for (j = 0; j < OBJ_SHARED_BULKHDR_LEN; j++) {
@@ -1794,6 +1801,7 @@ void initServer(void) {
     server.system_memory_size = zmalloc_get_memory_size();
 
     createSharedObjects();
+    initLazyfreeEngine();
     adjustOpenFilesLimit();
     server.el = aeCreateEventLoop(server.maxclients+CONFIG_FDSET_INCR);
     server.db = zmalloc(sizeof(redisDb)*server.dbnum);
@@ -1858,10 +1866,11 @@ void initServer(void) {
     server.repl_good_slaves_count = 0;
     updateCachedTime();
 
-    /* Create the serverCron() time event, that's our main way to process
-     * background operations. */
-    if(aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
-        serverPanic("Can't create the serverCron time event.");
+    /* Create out timers, that's our main way to process background
+     * operations. */
+    if(aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR ||
+       aeCreateTimeEvent(server.el, 1, lazyfreeCron, NULL, NULL) == AE_ERR) {
+        serverPanic("Can't create event loop timers.");
         exit(1);
     }
 
@@ -3268,10 +3277,15 @@ int freeMemoryIfNeeded(void) {
     size_t mem_used, mem_tofree, mem_freed;
     int slaves = listLength(server.slaves);
     mstime_t latency, eviction_latency;
+    long long delta;
+
+    /* Check if we are over the memory usage limit. If we are not, no need
+     * to subtract the slaves output buffers. We can just return ASAP. */
+    mem_used = zmalloc_used_memory();
+    if (mem_used <= server.maxmemory) return C_OK;
 
     /* Remove the size of slaves output buffers and AOF buffer from the
      * count of used memory. */
-    mem_used = zmalloc_used_memory();
     if (slaves) {
         listIter li;
         listNode *ln;
@@ -3291,15 +3305,36 @@ int freeMemoryIfNeeded(void) {
         mem_used -= aofRewriteBufferSize();
     }
 
-    /* Check if we are over the memory limit. */
+    /* Check if we are still over the memory limit. */
     if (mem_used <= server.maxmemory) return C_OK;
 
-    if (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)
-        return C_ERR; /* We need to free memory, but policy forbids. */
-
     /* Compute how much memory we need to free. */
     mem_tofree = mem_used - server.maxmemory;
     mem_freed = 0;
+
+    /* Let's start reclaiming memory from the lazy free list: those
+     * objects are logically freed so this is the first thing we want
+     * to get rid of. */
+    if (listLength(server.lazyfree_dbs) || listLength(server.lazyfree_obj)) {
+        latencyStartMonitor(eviction_latency);
+        while (mem_freed < mem_tofree) {
+            delta = (long long) zmalloc_used_memory();
+            size_t workdone = lazyfreeStep(LAZYFREE_STEP_FAST);
+            delta -= (long long) zmalloc_used_memory();
+            mem_freed += delta;
+            if (!workdone) break; /* Lazy free list is empty. */
+        }
+        latencyEndMonitor(eviction_latency);
+        latencyAddSampleIfNeeded("eviction-lazyfree",eviction_latency);
+    }
+
+    /* If after lazy freeing we are alraedy back to our limit, no need
+     * to evict keys. Return to the caller. */
+    if (mem_freed >= mem_tofree) return C_OK;
+
+    if (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)
+        return C_ERR; /* We need to free memory, but policy forbids. */
+
     latencyStartMonitor(latency);
     while (mem_freed < mem_tofree) {
         int j, k, keys_freed = 0;
@@ -3385,8 +3420,6 @@ int freeMemoryIfNeeded(void) {
 
             /* Finally remove the selected key. */
             if (bestkey) {
-                long long delta;
-
                 robj *keyobj = createStringObject(bestkey,sdslen(bestkey));
                 propagateExpire(db,keyobj);
                 /* We compute the amount of memory freed by dbDelete() alone.

src/server.h

@@ -185,27 +185,6 @@ typedef long long mstime_t; /* millisecond time type. */
 #define CMD_ASKING 4096               /* "k" flag */
 #define CMD_FAST 8192                 /* "F" flag */
 
-/* Object types */
-#define OBJ_STRING 0
-#define OBJ_LIST 1
-#define OBJ_SET 2
-#define OBJ_ZSET 3
-#define OBJ_HASH 4
-
-/* Objects encoding. Some kind of objects like Strings and Hashes can be
- * internally represented in multiple ways. The 'encoding' field of the object
- * is set to one of this fields for this object. */
-#define OBJ_ENCODING_RAW 0     /* Raw representation */
-#define OBJ_ENCODING_INT 1     /* Encoded as integer */
-#define OBJ_ENCODING_HT 2      /* Encoded as hash table */
-#define OBJ_ENCODING_ZIPMAP 3  /* Encoded as zipmap */
-#define OBJ_ENCODING_LINKEDLIST 4 /* Encoded as regular linked list */
-#define OBJ_ENCODING_ZIPLIST 5 /* Encoded as ziplist */
-#define OBJ_ENCODING_INTSET 6  /* Encoded as intset */
-#define OBJ_ENCODING_SKIPLIST 7  /* Encoded as skiplist */
-#define OBJ_ENCODING_EMBSTR 8  /* Embedded sds string encoding */
-#define OBJ_ENCODING_QUICKLIST 9 /* Encoded as linked list of ziplists */
-
 /* Defines related to the dump file format. To store 32 bits lengths for short
  * keys requires a lot of space, so we check the most significant 2 bits of
  * the first byte to interpreter the length:
@@ -441,9 +420,31 @@ typedef long long mstime_t; /* millisecond time type. */
 /* A redis object, that is a type able to hold a string / list / set */
 
 /* The actual Redis Object */
+#define OBJ_STRING 0
+#define OBJ_LIST 1
+#define OBJ_SET 2
+#define OBJ_ZSET 3
+#define OBJ_HASH 4
+
+/* Objects encoding. Some kind of objects like Strings and Hashes can be
+ * internally represented in multiple ways. The 'encoding' field of the object
+ * is set to one of this fields for this object. */
+#define OBJ_ENCODING_RAW 0     /* Raw representation */
+#define OBJ_ENCODING_INT 1     /* Encoded as integer */
+#define OBJ_ENCODING_HT 2      /* Encoded as hash table */
+#define OBJ_ENCODING_ZIPMAP 3  /* Encoded as zipmap */
+#define OBJ_ENCODING_LINKEDLIST 4 /* Encoded as regular linked list */
+#define OBJ_ENCODING_ZIPLIST 5 /* Encoded as ziplist */
+#define OBJ_ENCODING_INTSET 6  /* Encoded as intset */
+#define OBJ_ENCODING_SKIPLIST 7  /* Encoded as skiplist */
+#define OBJ_ENCODING_EMBSTR 8  /* Embedded sds string encoding */
+#define OBJ_ENCODING_QUICKLIST 9 /* Encoded as linked list of ziplists */
+
 #define LRU_BITS 24
 #define LRU_CLOCK_MAX ((1<<LRU_BITS)-1) /* Max value of obj->lru */
 #define LRU_CLOCK_RESOLUTION 1000 /* LRU clock resolution in ms */
+
+#define OBJ_SHARED_REFCOUNT INT_MAX
 typedef struct redisObject {
     unsigned type:4;
     unsigned encoding:4;
@@ -702,6 +703,10 @@ struct redisServer {
     int cronloops;              /* Number of times the cron function run */
     char runid[CONFIG_RUN_ID_SIZE+1];  /* ID always different at every exec. */
     int sentinel_mode;          /* True if this instance is a Sentinel. */
+    /* Lazy free */
+    list *lazyfree_dbs;         /* List of DBs to free in background. */
+    list *lazyfree_obj;         /* List of objects to free in background. */
+    size_t lazyfree_elements;   /* Number of logical element in obj list. */
     /* Networking */
     int port;                   /* TCP listening port */
     int tcp_backlog;            /* TCP listen() backlog */
@@ -1156,6 +1161,7 @@ void flagTransaction(client *c);
 void decrRefCount(robj *o);
 void decrRefCountVoid(void *o);
 void incrRefCount(robj *o);
+robj *makeObjectShared(robj *o);
 robj *resetRefCount(robj *obj);
 void freeStringObject(robj *o);
 void freeListObject(robj *o);
@@ -1376,6 +1382,7 @@ void dbOverwrite(redisDb *db, robj *key, robj *val);
 void setKey(redisDb *db, robj *key, robj *val);
 int dbExists(redisDb *db, robj *key);
 robj *dbRandomKey(redisDb *db);
+int dbSyncDelete(redisDb *db, robj *key);
 int dbDelete(redisDb *db, robj *key);
 robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o);
 long long emptyDb(void(callback)(void*));
@@ -1388,6 +1395,17 @@ unsigned int delKeysInSlot(unsigned int hashslot);
 int verifyClusterConfigWithData(void);
 void scanGenericCommand(client *c, robj *o, unsigned long cursor);
 int parseScanCursorOrReply(client *c, robj *o, unsigned long *cursor);
+void slotToKeyAdd(robj *key);
+void slotToKeyDel(robj *key);
+void slotToKeyFlush(void);
+
+/* Lazy free */
+#define LAZYFREE_STEP_SLOW 0
+#define LAZYFREE_STEP_FAST 1
+int dbAsyncDelete(redisDb *db, robj *key);
+void initLazyfreeEngine(void);
+size_t lazyfreeStep(int type);
+int lazyfreeCron(struct aeEventLoop *eventLoop, long long id, void *clientData);
 
 /* API to get key arguments from commands */
 int *getKeysFromCommand(struct redisCommand *cmd, robj **argv, int argc, int *numkeys);
@@ -1443,6 +1461,7 @@ void setexCommand(client *c);
 void psetexCommand(client *c);
 void getCommand(client *c);
 void delCommand(client *c);
+void unlinkCommand(client *c);
 void existsCommand(client *c);
 void setbitCommand(client *c);
 void getbitCommand(client *c);