提高MySQL 查詢效率的三個有效的嘗試(3)

　　使用連接池管理連接.

　　在有大量節點訪問的數據庫設計中,經常要使用到連接池來管理所有的連接.

　　一般方法是:建立兩個連接句柄隊列,空閒的等待使用的隊列和正在使用的隊列.

　　當要查詢時先從空閒隊列中獲取一個句柄,插入到正在使用的隊列,再用這個句柄做數據庫操作,完畢後一定要從使用隊列中刪除,再插入到空閒隊列.

　　設計代碼如下:

//定義句柄隊列
typedef std::list<MySQL *> CONNECTION_HANDLE_LIST;
typedef std::list<MySQL *>::iterator CONNECTION_HANDLE_LIST_IT;
 
//連接數據庫的參數結構
class CDBParameter            
{
public:
       char *host;                                 ///<主機名
       char *user;                                 ///<用戶名
       char *passWord;                         ///<密碼
       char *database;                           ///<數據庫名
       unsigned int port;                 ///<端口，一般為0
       const char *unix_socket;      ///<套接字，一般為NULL
       unsigned int clIEnt_flag; ///<一般為0
};
 
//創建兩個隊列
CONNECTION_HANDLE_LIST m_lsBusyList;                ///<正在使用的連接句柄
CONNECTION_HANDLE_LIST m_lsIdleList;                  ///<未使用的連接句柄
 
//所有的連接句柄先連上數據庫,加入到空閒隊列中,等待使用.
bool CDBManager::Connect(char * host /* = "localhost" */, char * user /* = "chenmin" */, \
                                           char * passWord /* = "chenmin" */, char * database /* = "HostCache" */)
{
       CDBParameter * lpDBParam = new CDBParameter();
       lpDBParam->host = host;
       lpDBParam->user = user;
       lpDBParam->password = passWord;
       lpDBParam->database = database;
       lpDBParam->port = 0;
       lpDBParam->unix_socket = NULL;
       lpDBParam->clIEnt_flag = 0;
       try
       {
              //連接
              for(int index = 0; index < CONNECTION_NUM; index++)
              {
                     MYSQL * pConnectHandle = mysql_init((MySQL*) 0);     //初始化連接句柄
                     if(!MySQL_real_connect(pConnectHandle, lpDBParam->host, lpDBParam->user, lpDBParam->passWord,\
       lpDBParam->database,lpDBParam->port,lpDBParam->unix_socket,lpDBParam->clIEnt_fla))
                            return false;
//加入到空閒隊列中
                     m_lsIdleList.push_back(pConnectHandle);
              }
       }
       catch(...)
       {
              return false;
       }
       return true;
}
 
//提取一個空閒句柄供使用
MySQL * CDBManager::GetIdleConnectHandle()
{
       MySQL * pConnectHandle = NULL;
       m_ListMutex.acquire();
       if(m_lsIdleList.size())
       {
              pConnectHandle = m_lsIdleList.front();      
              m_lsIdleList.pop_front();
              m_lsBusyList.push_back(pConnectHandle);
       }
       else //特殊情況,閒隊列中為空,返回為空
       {
              pConnectHandle = 0;
       }
       m_ListMutex.release();
 
       return pConnectHandle;
}
 
//從使用隊列中釋放一個使用完畢的句柄,插入到空閒隊列
void CDBManager::SetIdleConnectHandle(MySQL * connecthandle)
{
       m_ListMutex.acquire();
       m_lsBusyList.remove(connecthandle);
       m_lsIdleList.push_back(connecthandle);
       m_ListMutex.release();
}
//使用示例,首先獲取空閒句柄,利用這個句柄做真正的操作,然後再插回到空閒隊列
bool CDBManager::DeleteHostCacheBySessionID(char * sessionid)
{
       MySQL * pConnectHandle = GetIdleConnectHandle();
       if(!pConnectHandle)
              return 0;
       bool bRet = DeleteHostCacheBySessionID(pConnectHandle, sessionid);
       SetIdleConnectHandle(pConnectHandle);
       return bRet;
}
//傳入空閒的句柄,做真正的刪除操作
bool CDBManager::DeleteHostCacheBySessionID(MySQL * connecthandle, char * sessionid)
{
       char deleteSQL[SQL_LENGTH];
       memset(deleteSQL, 0, sizeof(deleteSQL));
       sprintf(deleteSQL,"delete from HostCache where SessionID = '%s'", sessionid);
       if(MySQL_query(connecthandle,deleteSQL) != 0) //刪除
              return false;
       return true;
}