use dictMerge() in endSnapshot for speed and cleaner code

Former-commit-id: ed8e10234e4499506f2557b0858dba86c30c9dc0

src/dict.cpp

@@ -42,6 +42,7 @@
 #include <stdarg.h>
 #include <limits.h>
 #include <sys/time.h>
+#include <algorithm>
 
 #include "dict.h"
 #include "zmalloc.h"
@@ -181,6 +182,12 @@ int dictMerge(dict *dst, dict *src)
     if (dictSize(src) == 0)
         return DICT_OK;
     
+    if (dictSize(dst) == 0)
+    {
+        std::swap(*dst, *src);
+        return DICT_OK;
+    }
+
     if (!dictIsRehashing(dst) && !dictIsRehashing(src))
     {
         dst->ht[1] = dst->ht[0];
@@ -190,6 +197,7 @@ int dictMerge(dict *dst, dict *src)
         return DICT_OK;
     }
 
+    dictExpand(dst, dictSize(dst)+dictSize(src));    // start dst rehashing if necessary
     auto &htDst = dictIsRehashing(dst) ? dst->ht[1] : dst->ht[0];
     for (int iht = 0; iht < 2; ++iht)
     {

src/snapshot.cpp

@@ -151,6 +151,8 @@ void redisDbPersistentData::endSnapshot(const redisDbPersistentDataSnapshot *psn
     m_spdbSnapshotHOLDER->m_refCount--;
     if (m_spdbSnapshotHOLDER->m_refCount > 0)
         return;
+
+    size_t sizeStart = size();
     serverAssert(m_spdbSnapshotHOLDER->m_refCount == 0);
     serverAssert((m_refCount == 0 && m_pdict->iterators == 0) || (m_refCount != 0 && m_pdict->iterators == 1));
 
@@ -189,25 +191,7 @@ void redisDbPersistentData::endSnapshot(const redisDbPersistentDataSnapshot *psn
     dictEmpty(m_pdictTombstone, nullptr);
 
     // Stage 2 Move all new keys to the snapshot DB
-    di = dictGetIterator(m_pdict);
+    dictMerge(m_spdbSnapshotHOLDER->m_pdict, m_pdict);
-    while ((de = dictNext(di)) != NULL)
-    {
-        robj *o = (robj*)dictGetVal(de);
-        sds newkey = sdsdupshared((sds)dictGetKey(de));
-        if (dictAdd(m_spdbSnapshotHOLDER->m_pdict, newkey, o) != DICT_OK)
-        {
-            // Review: We probably shouldn't even be getting into this state because the tombstone processing above should have cleared this out
-            sdsfree(newkey);
-            dictEntry *deExisting = dictFind(m_spdbSnapshotHOLDER->m_pdict, (const char*)dictGetKey(de));
-            serverAssert(deExisting != nullptr);
-            if (dictGetVal(deExisting) != nullptr)
-                decrRefCount((robj*)dictGetVal(deExisting));
-            dictSetVal(m_spdbSnapshotHOLDER->m_pdict, deExisting, o);
-        }
-
-        dictSetVal(m_pdict, de, nullptr);   // remove the object so free'ing the dict doesn't decRef the object
-    }
-    dictReleaseIterator(di);
     
     // Stage 3 swap the databases with the snapshot
     std::swap(m_pdict, m_spdbSnapshotHOLDER->m_pdict);
@@ -236,6 +220,7 @@ void redisDbPersistentData::endSnapshot(const redisDbPersistentDataSnapshot *psn
     serverAssert(m_pdbSnapshot == m_spdbSnapshotHOLDER.get() || m_pdbSnapshot == nullptr);
     serverAssert((m_refCount == 0 && m_pdict->iterators == 0) || (m_refCount != 0 && m_pdict->iterators == 1));
     serverAssert(m_spdbSnapshotHOLDER != nullptr || dictSize(m_pdictTombstone) == 0);
+    serverAssert(sizeStart == size());
 }
 
 dict_iter redisDbPersistentDataSnapshot::random_cache_threadsafe() const