提高MySQL 查詢效率的三個技巧第1/2頁

2020-01-19 00:24:13

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MySQL由于它本身的小巧和操作的高效, 在數(shù)據(jù)庫應用中越來越多的被采用.我在開發(fā)一個P2P應用的時候曾經(jīng)使用MySQL來保存P2P節(jié)點,由于P2P的應用中,結點數(shù)動輒上萬個,而且節(jié)點變化頻繁,因此一定要保持查詢和插入的高效.以下是我在使用過程中做的提高效率的三個有效的嘗試.

l        使用statement進行綁定查詢
使用statement可以提前構建查詢語法樹,在查詢時不再需要構建語法樹就直接查詢.因此可以很好的提高查詢的效率. 這個方法適合于查詢條件固定但查詢非常頻繁的場合.
使用方法是:
綁定, 創(chuàng)建一個MYSQL_STMT變量,與對應的查詢字符串綁定,字符串中的問號代表要傳入的變量,每個問號都必須指定一個變量.
查詢, 輸入每個指定的變量, 傳入MYSQL_STMT變量用可用的連接句柄執(zhí)行.
代碼如下:

//1.綁定
bool CDBManager::BindInsertStmt(MYSQL * connecthandle)
{
       //作插入操作的綁定
       MYSQL_BIND insertbind[FEILD_NUM];
       if(m_stInsertParam == NULL)
              m_stInsertParam = new CHostCacheTable;
       m_stInsertStmt = mysql_stmt_init(connecthandle);
       //構建綁定字符串
       char insertSQL[SQL_LENGTH];
       strcpy(insertSQL, "insert into HostCache(SessionID, ChannelID, ISPType, "
              "ExternalIP, ExternalPort, InternalIP, InternalPort) "
              "values(?, ?, ?, ?, ?, ?, ?)");
       mysql_stmt_prepare(m_stInsertStmt, insertSQL, strlen(insertSQL));
       int param_count= mysql_stmt_param_count(m_stInsertStmt);
       if(param_count != FEILD_NUM)
              return false;
       //填充bind結構數(shù)組, m_sInsertParam是這個statement關聯(lián)的結構變量
       memset(insertbind, 0, sizeof(insertbind));
       insertbind[0].buffer_type = MYSQL_TYPE_STRING;
       insertbind[0].buffer_length = ID_LENGTH /* -1 */;
       insertbind[0].buffer = (char *)m_stInsertParam->sessionid;
       insertbind[0].is_null = 0;
       insertbind[0].length = 0;

       insertbind[1].buffer_type = MYSQL_TYPE_STRING;
       insertbind[1].buffer_length = ID_LENGTH /* -1 */;
       insertbind[1].buffer = (char *)m_stInsertParam->channelid;
       insertbind[1].is_null = 0;
       insertbind[1].length = 0;

       insertbind[2].buffer_type = MYSQL_TYPE_TINY;
       insertbind[2].buffer = (char *)&m_stInsertParam->ISPtype;
       insertbind[2].is_null = 0;
       insertbind[2].length = 0;

       insertbind[3].buffer_type = MYSQL_TYPE_LONG;
       insertbind[3].buffer = (char *)&m_stInsertParam->externalIP;
       insertbind[3].is_null = 0;
       insertbind[3].length = 0;

       insertbind[4].buffer_type = MYSQL_TYPE_SHORT;
       insertbind[4].buffer = (char *)&m_stInsertParam->externalPort;
       insertbind[4].is_null = 0;
       insertbind[4].length = 0;

       insertbind[5].buffer_type = MYSQL_TYPE_LONG;
       insertbind[5].buffer = (char *)&m_stInsertParam->internalIP;
       insertbind[5].is_null = 0;
       insertbind[5].length = 0;

       insertbind[6].buffer_type = MYSQL_TYPE_SHORT;
       insertbind[6].buffer = (char *)&m_stInsertParam->internalPort;
       insertbind[6].is_null = 0;
       insertbind[6].is_null = 0;
       //綁定
       if (mysql_stmt_bind_param(m_stInsertStmt, insertbind))
              return false;
       return true;
}

//2.查詢
bool CDBManager::InsertHostCache2(MYSQL * connecthandle, char * sessionid, char * channelid, int ISPtype, /
              unsigned int eIP, unsigned short eport, unsigned int iIP, unsigned short iport)
{
       //填充結構變量m_sInsertParam
       strcpy(m_stInsertParam->sessionid, sessionid);
       strcpy(m_stInsertParam->channelid, channelid);
       m_stInsertParam->ISPtype = ISPtype;
       m_stInsertParam->externalIP = eIP;
       m_stInsertParam->externalPort = eport;
       m_stInsertParam->internalIP = iIP;
       m_stInsertParam->internalPort = iport;
       //執(zhí)行statement,性能瓶頸處
       if(mysql_stmt_execute(m_stInsertStmt))
              return false;
       return true;
}

l         隨機的獲取記錄
在某些數(shù)據(jù)庫的應用中, 我們并不是要獲取所有的滿足條件的記錄,而只是要隨機挑選出滿足條件的記錄. 這種情況常見于數(shù)據(jù)業(yè)務的統(tǒng)計分析,從大容量數(shù)據(jù)庫中獲取小量的數(shù)據(jù)的場合.
      有兩種方法可以做到
1.       常規(guī)方法,首先查詢出所有滿足條件的記錄,然后隨機的挑選出部分記錄.這種方法在滿足條件的記錄數(shù)很多時效果不理想.
2.       使用limit語法,先獲取滿足條件的記錄條數(shù), 然后在sql查詢語句中加入limit來限制只查詢滿足要求的一段記錄. 這種方法雖然要查詢兩次,但是在數(shù)據(jù)量大時反而比較高效.
示例代碼如下:

//1.常規(guī)的方法
//性能瓶頸,10萬條記錄時,執(zhí)行查詢140ms, 獲取結果集500ms,其余可忽略
int CDBManager::QueryHostCache(MYSQL* connecthandle, char * channelid, int ISPtype, CDBManager::CHostCacheTable * &hostcache)
{
       char selectSQL[SQL_LENGTH];
       memset(selectSQL, 0, sizeof(selectSQL));
       sprintf(selectSQL,"select * from HostCache where ChannelID = '%s' and ISPtype = %d", channelid, ISPtype);
       if(mysql_real_query(connecthandle, selectSQL, strlen(selectSQL)) != 0)   //檢索
              return 0;
       //獲取結果集
       m_pResultSet = mysql_store_result(connecthandle);
       if(!m_pResultSet)   //獲取結果集出錯
              return 0;
       int iAllNumRows = (int)(mysql_num_rows(m_pResultSet));      ///<所有的搜索結果數(shù)
       //計算待返回的結果數(shù)
       int iReturnNumRows = (iAllNumRows <= RETURN_QUERY_HOST_NUM)? iAllNumRows:RETURN_QUERY_HOST_NUM;
       if(iReturnNumRows <= RETURN_QUERY_HOST_NUM)
       {
              //獲取逐條記錄
              for(int i = 0; i<iReturnNumRows; i++)
              {
                     //獲取逐個字段
                     m_Row = mysql_fetch_row(m_pResultSet);
                     if(m_Row[0] != NULL)
                            strcpy(hostcache[i].sessionid, m_Row[0]);
                     if(m_Row[1] != NULL)
                            strcpy(hostcache[i].channelid, m_Row[1]);
                     if(m_Row[2] != NULL)
                            hostcache[i].ISPtype      = atoi(m_Row[2]);
                     if(m_Row[3] != NULL)
                            hostcache[i].externalIP   = atoi(m_Row[3]);
                     if(m_Row[4] != NULL)
                            hostcache[i].externalPort = atoi(m_Row[4]);
                     if(m_Row[5] != NULL)
                            hostcache[i].internalIP   = atoi(m_Row[5]);
                     if(m_Row[6] != NULL)
                            hostcache[i].internalPort = atoi(m_Row[6]);
              }
       }
       else
       {
              //隨機的挑選指定條記錄返回
              int iRemainder = iAllNumRows%iReturnNumRows;    ///<余數(shù)
              int iQuotient = iAllNumRows/iReturnNumRows;      ///<商
              int iStartIndex = rand()%(iRemainder + 1);         ///<開始下標
              //獲取逐條記錄
        for(int iSelectedIndex = 0; iSelectedIndex < iReturnNumRows; iSelectedIndex++)
        {
                            mysql_data_seek(m_pResultSet, iStartIndex + iQuotient * iSelectedIndex);
                            m_Row = mysql_fetch_row(m_pResultSet);
                  if(m_Row[0] != NULL)
                       strcpy(hostcache[iSelectedIndex].sessionid, m_Row[0]);
                   if(m_Row[1] != NULL)
                                   strcpy(hostcache[iSelectedIndex].channelid, m_Row[1]);
                   if(m_Row[2] != NULL)
                       hostcache[iSelectedIndex].ISPtype      = atoi(m_Row[2]);
                   if(m_Row[3] != NULL)
                       hostcache[iSelectedIndex].externalIP   = atoi(m_Row[3]);
                    if(m_Row[4] != NULL)
                       hostcache[iSelectedIndex].externalPort = atoi(m_Row[4]);
                   if(m_Row[5] != NULL)
                       hostcache[iSelectedIndex].internalIP   = atoi(m_Row[5]);
                   if(m_Row[6] != NULL)
                       hostcache[iSelectedIndex].internalPort = atoi(m_Row[6]);
        }
      }
       //釋放結果集內(nèi)容
       mysql_free_result(m_pResultSet);
       return iReturnNumRows;
}

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