Add build flag to disable MVCC tstamps

Former-commit-id: f17d178d03f44abcdaddd851a313dd3f7ec87ed5

src/Makefile

@@ -47,6 +47,11 @@ endif
 
 USEASM?=true
 
+ifeq ($(NOMVCC),)
+	CFLAGS+= -DENABLE_MVCC
+	CXXFLAGS+= -DENABLE_MVCC
+endif
+
 ifneq ($(SANITIZE),)
 	CFLAGS+= -fsanitize=$(SANITIZE) -DSANITIZE
 	CXXFLAGS+= -fsanitize=$(SANITIZE) -DSANITIZE

src/db.cpp

@@ -92,9 +92,11 @@ static robj *lookupKey(redisDb *db, robj *key, int flags) {
 
         updateDbValAccess(de, flags);
 
+#ifdef ENABLE_MVCC
         if (flags & LOOKUP_UPDATEMVCC) {
             val->mvcc_tstamp = getMvccTstamp();
         }
+#endif
         return val;
     } else {
         return NULL;
@@ -206,7 +208,9 @@ int dbAddCore(redisDb *db, robj *key, robj *val) {
     serverAssert(!val->FExpires());
     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)
     {
@@ -256,7 +260,9 @@ void dbOverwriteCore(redisDb *db, dictEntry *de, robj *key, robj *val, bool fUpd
     if (fUpdateMvcc) {
         if (val->getrefcount(std::memory_order_relaxed) == OBJ_SHARED_REFCOUNT)
             val = dupStringObject(val);
+#ifdef ENABLE_MVCC
         val->mvcc_tstamp = getMvccTstamp();
+#endif
     }
 
     dictSetVal(db->pdict, de, val);
@@ -290,12 +296,14 @@ int dbMerge(redisDb *db, robj *key, robj *val, int fReplace)
         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)
         {
             dbOverwriteCore(db, de, key, val, false, true);
             return true;
         }
+#endif
 
         return false;
     }

src/object.cpp

@@ -46,7 +46,9 @@ robj *createObject(int type, void *ptr) {
     o->encoding = OBJ_ENCODING_RAW;
     o->m_ptr = ptr;
     o->setrefcount(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. */
@@ -101,7 +103,9 @@ robj *createEmbeddedStringObject(const char *ptr, size_t len) {
     o->type = OBJ_STRING;
     o->encoding = OBJ_ENCODING_EMBSTR;
     o->setrefcount(1);
+#ifdef ENABLE_MVCC
     o->mvcc_tstamp = OBJ_MVCC_INVALID;
+#endif
 
     if (g_pserver->maxmemory_policy & MAXMEMORY_FLAG_LFU) {
         o->lru = (LFUGetTimeInMinutes()<<8) | LFU_INIT_VAL;
@@ -129,8 +133,13 @@ robj *createEmbeddedStringObject(const char *ptr, size_t len) {
  *
  * The current limit of 52 is chosen so that the biggest string object
  * we allocate as EMBSTR will still fit into the 64 byte arena of jemalloc. */
+#ifdef ENABLE_MVCC
 #define OBJ_ENCODING_EMBSTR_SIZE_LIMIT 48
-static_assert((sizeof(redisObject)+OBJ_ENCODING_EMBSTR_SIZE_LIMIT-8) == 64, "Max EMBSTR obj should be 64 bytes total");
+#else
+#define OBJ_ENCODING_EMBSTR_SIZE_LIMIT 256
+#endif
+
+//static_assert((sizeof(redisObject)+OBJ_ENCODING_EMBSTR_SIZE_LIMIT-8) == 64, "Max EMBSTR obj should be 64 bytes total");
 robj *createStringObject(const char *ptr, size_t len) {
     if (len <= OBJ_ENCODING_EMBSTR_SIZE_LIMIT)
         return createEmbeddedStringObject(ptr,len);
@@ -1317,10 +1326,12 @@ NULL
          * because we update the access time only
          * when the key is read or overwritten. */
         addReplyLongLong(c,LFUDecrAndReturn(o));
+#ifdef ENABLE_MVCC
     } else if (!strcasecmp(szFromObj(c->argv[1]), "lastmodified") && c->argc == 3) {
         if ((o = objectCommandLookupOrReply(c,c->argv[2],shared.null[c->resp]))
                 == NULL) return;
         addReplyLongLong(c, (g_pserver->mstime - (o->mvcc_tstamp >> MVCC_MS_SHIFT)) / 1000);
+#endif
     } else {
         addReplySubcommandSyntaxError(c);
     }

src/rdb.cpp

@@ -1089,8 +1089,10 @@ int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val, expireEntry *pexpire) {
     }
 
     char szT[32];
+#ifdef ENABLE_MVCC
     snprintf(szT, 32, "%" PRIu64, val->mvcc_tstamp);
     if (rdbSaveAuxFieldStrStr(rdb,"mvcc-tstamp", szT) == -1) return -1;
+#endif
 
     /* Save type, key, value */
     if (rdbSaveObjectType(rdb,val) == -1) return -1;
@@ -2046,7 +2048,9 @@ robj *rdbLoadObject(int rdbtype, rio *rdb, sds key, uint64_t mvcc_tstamp) {
         return NULL;
     }
 
+#ifdef ENABLE_MVCC
     o->mvcc_tstamp = mvcc_tstamp;
+#endif
     serverAssert(!o->FExpires());
     return o;
 }
@@ -2398,7 +2402,11 @@ int rdbLoadRio(rio *rdb, int rdbflags, rdbSaveInfo *rsi) {
             key = nullptr;
             goto eoferr;
         }
+#ifdef ENABLE_MVCC
         bool fStaleMvccKey = (rsi) ? val->mvcc_tstamp < rsi->mvccMinThreshold : false;
+#else
+        bool fStaleMvccKey = false;
+#endif
 
         /* Check if the key already expired. This function is used when loading
          * an RDB file from disk, either at startup, or when an RDB was

src/server.h

@@ -805,7 +805,9 @@ typedef struct redisObject {
 private:
     mutable std::atomic<unsigned> refcount {0};
 public:
+#ifdef ENABLE_MVCC
     uint64_t mvcc_tstamp;
+#endif
     void *m_ptr;
 
     inline bool FExpires() const { return refcount.load(std::memory_order_relaxed) >> 31; }
@@ -816,7 +818,11 @@ public:
     void addref() const { refcount.fetch_add(1, std::memory_order_relaxed); }
     unsigned release() const { return refcount.fetch_sub(1, std::memory_order_seq_cst) & ~(1U << 31); }
 } robj;
+#ifdef ENABLE_MVCC
 static_assert(sizeof(redisObject) == 24, "object size is critical, don't increase");
+#else
+static_assert(sizeof(redisObject) == 16, "object size is critical, don't increase");
+#endif
 
 __attribute__((always_inline)) inline const void *ptrFromObj(robj_roptr &o)
 {

src/storage.h

@@ -1,8 +1,6 @@
 #ifndef __STORAGE_H__
 #define __STORAGE_H__
 
-#define OBJ_ENCODING_EMBSTR_SIZE_LIMIT 48   // Note: also defined in object.c - should always match
-
 #ifdef __cplusplus
 extern "C" {
 #endif