Timestamp writes to objects so we can be smarter about merging databases

Former-commit-id: 5dc9f70386617b02fab7eee1194f321f6b4b25c5

src/Makefile

@@ -44,8 +44,6 @@ endif
 endif
 endif
 
-# CXXFLAGS+= -DENABLE_MVCC
-
 USEASM?=true
 # Do we use our assembly spinlock? X64 only
 ifeq ($(uname_S),Linux)

src/db.cpp

@@ -70,6 +70,10 @@ static robj *lookupKey(redisDb *db, robj *key, int flags) {
                 val->lru = LRU_CLOCK();
             }
         }
+
+        if (flags & LOOKUP_UPDATEMVCC) {
+            val->mvcc_tstamp = getMvccTstamp();
+        }
         return val;
     } else {
         return NULL;
@@ -157,7 +161,7 @@ robj_roptr lookupKeyRead(redisDb *db, robj *key) {
  * does not exist in the specified DB. */
 robj *lookupKeyWrite(redisDb *db, robj *key) {
     expireIfNeeded(db,key);
-    return lookupKey(db,key,LOOKUP_NONE);
+    return lookupKey(db,key,LOOKUP_UPDATEMVCC);
 }
 
 robj_roptr lookupKeyReadOrReply(client *c, robj *key, robj *reply) {
@@ -175,9 +179,7 @@ robj *lookupKeyWriteOrReply(client *c, robj *key, robj *reply) {
 int dbAddCore(redisDb *db, robj *key, robj *val) {
     sds copy = sdsdup(szFromObj(key));
     int retval = dictAdd(db->pdict, copy, val);
-#ifdef ENABLE_MVCC
     val->mvcc_tstamp = key->mvcc_tstamp = getMvccTstamp();
-#endif
 
     if (retval == DICT_OK)
     {
@@ -211,12 +213,9 @@ void dbOverwriteCore(redisDb *db, dictEntry *de, robj *val, bool fUpdateMvcc)
     if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
         val->lru = old->lru;
     }
-#ifdef ENABLE_MVCC
     if (fUpdateMvcc)
         val->mvcc_tstamp = getMvccTstamp();
-#else
-    UNUSED(fUpdateMvcc);
-#endif
+
     dictSetVal(db->pdict, de, val);
 
     if (server.lazyfree_lazy_server_del) {
@@ -247,14 +246,14 @@ int dbMerge(redisDb *db, robj *key, robj *val, int fReplace)
         dictEntry *de = dictFind(db->pdict, ptrFromObj(key));
         if (de == nullptr)
             return (dbAddCore(db, key, val) == DICT_OK);
-#ifdef ENABLE_MVCC
+
         robj *old = (robj*)dictGetVal(de);
         if (old->mvcc_tstamp <= val->mvcc_tstamp)
-#endif
         {
             dbOverwriteCore(db, de, val, false);
             return true;
         }
+        
         return false;
     }
     else

src/object.cpp

@@ -44,9 +44,7 @@ robj *createObject(int type, void *ptr) {
     o->encoding = OBJ_ENCODING_RAW;
     o->m_ptr = ptr;
     o->refcount = 1;
-#ifdef ENABLE_MVCC
     o->mvcc_tstamp = OBJ_MVCC_INVALID;
-#endif
 
     /* Set the LRU to the current lruclock (minutes resolution), or
      * alternatively the LFU counter. */
@@ -94,9 +92,8 @@ robj *createEmbeddedStringObject(const char *ptr, size_t len) {
     o->type = OBJ_STRING;
     o->encoding = OBJ_ENCODING_EMBSTR;
     o->refcount = 1;
-#ifdef ENABLE_MVCC
     o->mvcc_tstamp = OBJ_MVCC_INVALID;
-#endif
+
     if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
         o->lru = (LFUGetTimeInMinutes()<<8) | LFU_INIT_VAL;
     } else {

src/rdb.cpp

@@ -1061,11 +1061,9 @@ int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val, long long expiretime) {
         if (rdbWriteRaw(rdb,buf,1) == -1) return -1;
     }
 
-#ifdef ENABLE_MVCC
     char szMvcc[32];
     snprintf(szMvcc, 32, "%" PRIu64, val->mvcc_tstamp);
     if (rdbSaveAuxFieldStrStr(rdb,"mvcc-tstamp", szMvcc) == -1) return -1;
-#endif
 
     /* Save type, key, value */
     if (rdbSaveObjectType(rdb,val) == -1) return -1;
@@ -1822,11 +1820,8 @@ robj *rdbLoadObject(int rdbtype, rio *rdb, robj *key, uint64_t mvcc_tstamp) {
     } else {
         rdbExitReportCorruptRDB("Unknown RDB encoding type %d",rdbtype);
     }
-#ifdef ENABLE_MVCC
+
     o->mvcc_tstamp = mvcc_tstamp;
-#else
-    UNUSED(mvcc_tstamp);
-#endif
     return o;
 }
 

src/server.cpp

@@ -2933,6 +2933,8 @@ void initServer(void) {
     server.aof_last_write_errno = 0;
     server.repl_good_slaves_count = 0;
 
+    server.mvcc_tstamp = 0;
+
     /* Create the timer callback, this is our way to process many background
      * operations incrementally, like clients timeout, eviction of unaccessed
      * expired keys and so forth. */
@@ -3423,6 +3425,7 @@ int processCommand(client *c, int callFlags) {
 
     AssertCorrectThread(c);
     serverAssert(GlobalLocksAcquired());
+    incrementMvccTstamp();
 
     /* Now lookup the command and check ASAP about trivial error conditions
      * such as wrong arity, bad command name and so forth. */
@@ -4879,7 +4882,20 @@ int redisIsSupervised(int mode) {
 
 uint64_t getMvccTstamp()
 {
-    return (server.mstime << 16);
+    return server.mvcc_tstamp;
+}
+
+void incrementMvccTstamp()
+{
+    uint64_t msPrev = server.mvcc_tstamp >> 22;
+    if (msPrev >= (uint64_t)server.mstime)  // we can be greater if the count overflows
+    {
+        atomicIncr(server.mvcc_tstamp, 1);
+    }
+    else
+    {
+        server.mvcc_tstamp = ((uint64_t)server.mstime) << 22;
+    }
 }
 
 void *workerThreadMain(void *parg)

src/server.h

@@ -709,10 +709,8 @@ typedef struct redisObject {
     unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
                             * LFU data (least significant 8 bits frequency
                             * and most significant 16 bits access time). */
-#ifdef ENABLE_MVCC
-    uint64_t mvcc_tstamp;
-#endif
     mutable int refcount;
+    uint64_t mvcc_tstamp;
     void *m_ptr;
 } robj;
 
@@ -1526,6 +1524,7 @@ struct redisServer {
     unsigned char uuid[UUID_BINARY_LEN];         /* This server's UUID - populated on boot */
 
     struct fastlock flock;
+    uint64_t mvcc_tstamp;
 };
 
 typedef struct pubsubPattern {
@@ -2136,6 +2135,7 @@ void objectSetLRUOrLFU(robj *val, long long lfu_freq, long long lru_idle,
                        long long lru_clock);
 #define LOOKUP_NONE 0
 #define LOOKUP_NOTOUCH (1<<0)
+#define LOOKUP_UPDATEMVCC (1<<1)
 void dbAdd(redisDb *db, robj *key, robj *val);
 void dbOverwrite(redisDb *db, robj *key, robj *val);
 int dbMerge(redisDb *db, robj *key, robj *val, int fReplace);
@@ -2447,6 +2447,7 @@ struct redisMaster *MasterInfoFromClient(client *c);
 
 /* MVCC */
 uint64_t getMvccTstamp();
+void incrementMvccTstamp();
 
 #if defined(__GNUC__)
 #ifndef __cplusplus