mysql如何实现本地keyvalue数据库缓存示例

Key-Value缓存有很多，用的较多的是memcache、redis，他们都是以独立服务的形式运行，在工作中有时需要嵌入一个本地的key-value缓存，当然已经有LevelDb等，但感觉还是太重量级了。

本文实现了一种超级轻量的缓存，

1、实现代码仅仅需要400行；

2、性能高效，value长度在1K时测试速度在每秒200万左右

3、缓存是映射到文件中的，所以没有malloc、free的开销，以及带来的内存泄露、内存碎片等；

4、如果服务挂掉了，重启后缓存内容继续存在；

5、如果把缓存映射到磁盘文件就算机器挂了，缓存中内容还是会存在，当然有可能会出现数据损坏的情况；

6、一定程度上实现了LRU淘汰算法，实现的LRU不是全局的只是一条链上的，所以只能说在一定程序上实现了；

7、稳定，已经在多个项目中运用，线上部署的机器有几十台，运行了大半年了没出过问题；

8、普通的缓存key、value都是字符串的形式，此缓存的key、value都可以是class、struct对象结构使用更方便；

老规矩直接上代码：

template<typename K, typename V>
class HashTable
{
public:
 HashTable(const char *tablename, uint32_t tableLen, uint32_t nodeTotal);
 virtual ~HashTable(); bool Add(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); //check is exist
 uint32_t nodeId = GetIdByKey(key);
 if(nodeId != m_InvalidId) return false; nodeId = GetFreeNode();
 if(nodeId == m_InvalidId) return false; uint32_t hashCode = key.HashCode();
 Entry *tmpNode = m_EntryAddr + nodeId;
 tmpNode->m_Key = key;
 tmpNode->m_Code = hashCode;
 tmpNode->m_Value = value; uint32_t index = hashCode % m_HeadAddr->m_TableLen;
 AddNodeToHead(index, nodeId); return true;
 } bool Del(K &key)
 {
 AutoLock autoLock(m_MutexLock); uint32_t nodeId = GetIdByKey(key);
 if(nodeId == m_InvalidId) return false; uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen; return RecycleNode(index, nodeId);
 } bool Set(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); uint32_t nodeId = GetIdByKey(key);
 if(nodeId == m_InvalidId) return false; (m_EntryAddr + nodeId)->m_Value = value; return true;
 } bool Get(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); uint32_t nodeId = GetIdByKey(key);
 if(nodeId == m_InvalidId) return false; value = (m_EntryAddr + nodeId)->m_Value; return true;
 } bool Exist(K &key)
 {
 AutoLock autoLock(m_MutexLock); uint32_t nodeId = GetIdByKey(key);
 if(nodeId == m_InvalidId) return false; return true;
 } uint32_t Count()
 {
 AutoLock autoLock(m_MutexLock);
 return m_HeadAddr->m_UsedCount;
 } //if exist set else add
 bool Replace(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); if(Exist(key)) return Set(key, value);
 else return Add(key, value);
 } /***********************************************
 ****LRU: when visit a node, move it to head ****
 ************************************************/
 //if no empty place,recycle tail
 bool LruAdd(K &key, V &value, K &recyKey, V &recyValue, bool &recycled)
 {
 AutoLock autoLock(m_MutexLock); if(Exist(key)) return false; if(Add(key, value)) return true; uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen;
 uint32_t tailId = GetTailNodeId(index); if(tailId == m_InvalidId) return false; Entry *tmpNode = m_EntryAddr + tailId;
 recyKey = tmpNode->m_Key;
 recyValue = tmpNode->m_Value;
 recycled = true; RecycleNode(index, tailId); return Add(key, value);
 } bool LruSet(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); if(Set(key, value)) return MoveToHead(key);
 else return false;
 } bool LruGet(K &key, V &value)
 {
 AutoLock autoLock(m_MutexLock); if(Get(key, value)) return MoveToHead(key);
 else return false;
 } //if exist set else add; if add failed recycle tail than add
 bool LruReplace(K &key, V &value, K &recyKey, V &recyValue, bool &recycled)
 {
 AutoLock autoLock(m_MutexLock); recycled = false; if(Exist(key)) return LruSet(key, value);
 else return LruAdd(key, value, recyKey, recyValue, recycled);
 } void Clear()
 {
 AutoLock autoLock(m_MutexLock); m_HeadAddr->m_FreeBase = 0;
 m_HeadAddr->m_RecycleHead = 0;
 m_HeadAddr->m_UsedCount = 0;
 for(uint32_t i = 0; i < m_HeadAddr->m_TableLen; ++i)
 {
 (m_ArrayAddr+i)->m_Head = m_InvalidId;
 (m_ArrayAddr+i)->m_Tail = m_InvalidId;
 }
 } int GetRowKeys(vector<K> &keys, uint32_t index)
 {
 AutoLock autoLock(m_MutexLock); if(index >= m_HeadAddr->m_TableLen) return -1; keys.clear();
 keys.reserve(16); int count = 0;
 Array *tmpArray = m_ArrayAddr + index;
 uint32_t nodeId = tmpArray->m_Head;
 while(nodeId != m_InvalidId)
 {
 Entry *tmpNode = m_EntryAddr + nodeId;
 keys.push_back(tmpNode->m_Key);
 nodeId = tmpNode->m_Next;
 ++count;
 } return count;
 } void *Padding(uint32_t size)
 {
 AutoLock autoLock(m_MutexLock); if(size > m_HeadSize - sizeof(TableHead)) return NULL;
 else return m_HeadAddr->m_Padding;
 }private:
 static const uint32_t m_InvalidId = 0xffffffff;
 static const uint32_t m_HeadSize = 1024;
 struct TableHead
 {
 uint32_t m_TableLen;
 uint32_t m_NodeTotal;
 uint32_t m_FreeBase;
 uint32_t m_RecycleHead;
 uint32_t m_UsedCount;
 char m_TableName[256];
 uint32_t m_Padding[0];
 }; struct Array
 {
 uint32_t m_Head;
 uint32_t m_Tail;
 }; struct Entry
 {
 V m_Value;
 K m_Key;
 uint32_t m_Code;
 uint32_t m_Next;
 uint32_t m_Prev;
 }; size_t m_MemSize;
 uint8_t *m_MemAddr;
 TableHead *m_HeadAddr;
 Array *m_ArrayAddr;
 Entry *m_EntryAddr; ThreadMutex m_MutexLock; bool MoveToHead(K &key);
 uint32_t GetIdByKey(K &key);
 void AddNodeToHead(uint32_t index, uint32_t nodeId);
 bool MoveNodeToHead(uint32_t index, uint32_t nodeId);
 bool RecycleNode(uint32_t index, uint32_t nodeId);
 uint32_t GetTailNodeId(uint32_t index);
 uint32_t GetFreeNode(); DISABLE_COPY_AND_ASSIGN(HashTable);
};template<typename K, typename V>
HashTable<K, V>::HashTable(const char *tablename, uint32_t tableLen, uint32_t nodeTotal)
{
 AbortAssert(tablename != NULL); m_MemSize = m_HeadSize + tableLen*sizeof(Array) + nodeTotal*sizeof(Entry);
 m_MemAddr = (uint8_t*)MemFile::Realloc(tablename, m_MemSize);
 AbortAssert(m_MemAddr != NULL); m_HeadAddr = (TableHead*)(m_MemAddr);
 m_ArrayAddr = (Array*)(m_MemAddr + m_HeadSize);
 m_EntryAddr = (Entry*)(m_MemAddr + m_HeadSize + tableLen*sizeof(Array)); m_HeadAddr->m_TableLen = tableLen;
 m_HeadAddr->m_NodeTotal = nodeTotal;
 strncpy(m_HeadAddr->m_TableName, tablename, sizeof(m_HeadAddr->m_TableName)); if(m_HeadAddr->m_UsedCount == 0)//if first use init array to invalid id 
 {
 for(uint32_t i = 0; i < tableLen; ++i)
 {
 (m_ArrayAddr+i)->m_Head = m_InvalidId;
 (m_ArrayAddr+i)->m_Tail = m_InvalidId;
 } m_HeadAddr->m_FreeBase = 0;
 m_HeadAddr->m_RecycleHead = 0;
 }
}template<typename K, typename V>
HashTable<K, V>::~HashTable()
{
 MemFile::Release(m_MemAddr, m_MemSize);
}template<typename K, typename V>
bool HashTable<K, V>::MoveToHead(K &key)
{
 uint32_t nodeId = GetIdByKey(key);
 uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen; return MoveNodeToHead(index, nodeId);
}template<typename K, typename V>
uint32_t HashTable<K, V>::GetIdByKey(K &key)
{
 uint32_t hashCode = key.HashCode();
 uint32_t index = hashCode % m_HeadAddr->m_TableLen;
 Array *tmpArray = m_ArrayAddr + index; uint32_t nodeId = tmpArray->m_Head;
 while(nodeId != m_InvalidId)
 {
 Entry *tmpNode = m_EntryAddr + nodeId;
 if(tmpNode->m_Code == hashCode && key.Equals(tmpNode->m_Key)) break; nodeId = tmpNode->m_Next;
 } return nodeId;
}template<typename K, typename V>
void HashTable<K, V>::AddNodeToHead(uint32_t index, uint32_t nodeId)
{
 if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return; Array *tmpArray = m_ArrayAddr + index;
 Entry *tmpNode = m_EntryAddr + nodeId;
 if(m_InvalidId == tmpArray->m_Head)
 {
 tmpArray->m_Head = nodeId;
 tmpArray->m_Tail = nodeId;
 }
 else
 {
 tmpNode->m_Next = tmpArray->m_Head;
 (m_EntryAddr + tmpArray->m_Head)->m_Prev = nodeId;
 tmpArray->m_Head = nodeId;
 }
}template<typename K, typename V>
bool HashTable<K, V>::MoveNodeToHead(uint32_t index, uint32_t nodeId)
{
 if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return false; Array *tmpArray = m_ArrayAddr + index;
 Entry *tmpNode = m_EntryAddr + nodeId; //already head
 if(tmpArray->m_Head == nodeId)
 {
 return true;
 } uint32_t nodePrev = tmpNode->m_Prev;
 uint32_t nodeNext = tmpNode->m_Next;
 (m_EntryAddr+nodePrev)->m_Next = nodeNext;
 if(nodeNext != m_InvalidId)
 {
 (m_EntryAddr+nodeNext)->m_Prev = nodePrev;
 }
 else
 {
 tmpArray->m_Tail = nodePrev;
 } tmpNode->m_Prev = m_InvalidId;
 tmpNode->m_Next = tmpArray->m_Head;
 (m_EntryAddr + tmpArray->m_Head)->m_Prev = nodeId;
 tmpArray->m_Head = nodeId; return true;
}template<typename K, typename V>
bool HashTable<K, V>::RecycleNode(uint32_t index, uint32_t nodeId)
{
 if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return false; Array *tmpArray = m_ArrayAddr + index;
 Entry *tmpNode = m_EntryAddr + nodeId; uint32_t nodePrev = tmpNode->m_Prev;
 uint32_t nodeNext = tmpNode->m_Next; if(nodePrev != m_InvalidId)
 {
 (m_EntryAddr + nodePrev)->m_Next = nodeNext;
 }
 else
 {
 tmpArray->m_Head = nodeNext;
 } if(nodeNext != m_InvalidId)
 {
 (m_EntryAddr + nodeNext)->m_Prev = nodePrev;
 }
 else
 {
 tmpArray->m_Tail = nodePrev;
 } (m_EntryAddr+nodeId)->m_Next = m_HeadAddr->m_RecycleHead;
 m_HeadAddr->m_RecycleHead = nodeId;
 --(m_HeadAddr->m_UsedCount); return true;
}template<typename K, typename V>
uint32_t HashTable<K, V>::GetTailNodeId(uint32_t index)
{
 if(index >= m_HeadAddr->m_TableLen) return m_InvalidId; Array *tmpArray = m_ArrayAddr + index; return tmpArray->m_Tail;
}template<typename K, typename V>
uint32_t HashTable<K, V>::GetFreeNode()
{
 uint32_t nodeId = m_InvalidId;
 if(m_HeadAddr->m_UsedCount < m_HeadAddr->m_FreeBase)//get from recycle list
 {
 nodeId = m_HeadAddr->m_RecycleHead;
 m_HeadAddr->m_RecycleHead = (m_EntryAddr+nodeId)->m_Next;
 ++(m_HeadAddr->m_UsedCount);
 }
 else if(m_HeadAddr->m_UsedCount < m_HeadAddr->m_NodeTotal)//get from free mem
 {
 nodeId = m_HeadAddr->m_FreeBase;
 ++(m_HeadAddr->m_FreeBase);
 ++(m_HeadAddr->m_UsedCount);
 }
 else
 {
 nodeId = m_InvalidId;
 } //init node
 if(nodeId < m_HeadAddr->m_NodeTotal)
 {
 Entry *tmpNode = m_EntryAddr + nodeId;
 memset(tmpNode, 0, sizeof(Entry)); tmpNode->m_Next = m_InvalidId;
 tmpNode->m_Prev = m_InvalidId;
 } return nodeId;
}

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