提高MySQL 查詢效率的三個技巧小結
MySQL由于它本身的小巧和操作的高效, 在數據庫應用中越來越多的被采用.我在開發一個P2P應用的時候曾經使用MySQL來保存P2P節點,由于P2P的應用中,結點數動輒上萬個,而且節點變化頻繁,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行.
代碼如下:
復制代碼代碼如下:
//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結構數組, m_sInsertParam是這個statement關聯的結構變量
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;
//執行statement,性能瓶頸處
if(mysql_stmt_execute(m_stInsertStmt))
return false;
return true;
}
隨機的獲取記錄
在某些數據庫的應用中, 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. 這種情況常見于數據業務的統計分析,從大容量數據庫中獲取小量的數據的場合.
有兩種方法可以做到
1. 常規方法,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, 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,但是在數據量大時反而比較高效.
示例代碼如下:
復制代碼代碼如下:
//1.常規的方法
//性能瓶頸,10萬條記錄時,執行查詢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
//計算待返回的結果數
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
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]);
}
}
//釋放結果集內容
mysql_free_result(m_pResultSet);
return iReturnNumRows;
}
//2.使用limit版
int CDBManager::QueryHostCache(MYSQL * connecthandle, char * channelid, unsigned int myexternalip, int ISPtype, CHostCacheTable * hostcache)
{
//首先獲取滿足結果的記錄條數,再使用limit隨機選擇指定條記錄返回
MYSQL_ROW row;
MYSQL_RES * pResultSet;
char selectSQL[SQL_LENGTH];
memset(selectSQL, 0, sizeof(selectSQL));
sprintf(selectSQL,"select count(*) from HostCache where ChannelID = '%s' and ISPtype = %d", channelid, ISPtype);
if(mysql_real_query(connecthandle, selectSQL, strlen(selectSQL)) != 0) //檢索
return 0;
pResultSet = mysql_store_result(connecthandle);
if(!pResultSet)
return 0;
row = mysql_fetch_row(pResultSet);
int iAllNumRows = atoi(row[0]);
mysql_free_result(pResultSet);
//計算待取記錄的上下范圍
int iLimitLower = (iAllNumRows <= RETURN_QUERY_HOST_NUM)?
0:(rand()%(iAllNumRows - RETURN_QUERY_HOST_NUM));
int iLimitUpper = (iAllNumRows <= RETURN_QUERY_HOST_NUM)?
iAllNumRows:(iLimitLower + RETURN_QUERY_HOST_NUM);
//計算待返回的結果數
int iReturnNumRows = (iAllNumRows <= RETURN_QUERY_HOST_NUM)?
iAllNumRows:RETURN_QUERY_HOST_NUM;
//使用limit作查詢
sprintf(selectSQL,"select SessionID, ExternalIP, ExternalPort, InternalIP, InternalPort "
"from HostCache where ChannelID = '%s' and ISPtype = %d limit %d, %d"
, channelid, ISPtype, iLimitLower, iLimitUpper);
if(mysql_real_query(connecthandle, selectSQL, strlen(selectSQL)) != 0) //檢索
return 0;
pResultSet = mysql_store_result(connecthandle);
if(!pResultSet)
return 0;
//獲取逐條記錄
for(int i = 0; i<iReturnNumRows; i++)
{
//獲取逐個字段
row = mysql_fetch_row(pResultSet);
if(row[0] != NULL)
strcpy(hostcache[i].sessionid, row[0]);
if(row[1] != NULL)
hostcache[i].externalIP = atoi(row[1]);
if(row[2] != NULL)
hostcache[i].externalPort = atoi(row[2]);
if(row[3] != NULL)
hostcache[i].internalIP = atoi(row[3]);
if(row[4] != NULL)
hostcache[i].internalPort = atoi(row[4]);
}
//釋放結果集內容
mysql_free_result(pResultSet);
return iReturnNumRows;
}
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,空閑的等待使用的隊列和正在使用的隊列.
當要查詢時先從空閑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,完畢后一定要從使用隊列中刪除,再插入到空閑隊列.
設計代碼如下:
復制代碼代碼如下:
//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,加入到空閑隊列中,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;
//加入到空閑隊列中
m_lsIdleList.push_back(pConnectHandle);
}
}
catch(...)
{
return false;
}
return true;
}
//提取一個空閑句柄供使用
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,閑隊列中為空,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,插入到空閑隊列
void CDBManager::SetIdleConnectHandle(MYSQL * connecthandle)
{
m_ListMutex.acquire();
m_lsBusyList.remove(connecthandle);
m_lsIdleList.push_back(connecthandle);
m_ListMutex.release();
}
//使用示例,首先獲取空閑句柄,利用這個句柄做真正的操作,然后再插回到空閑隊列
bool CDBManager::DeleteHostCacheBySessionID(char * sessionid)
{
MYSQL * pConnectHandle = GetIdleConnectHandle();
if(!pConnectHandle)
return 0;
bool bRet = DeleteHostCacheBySessionID(pConnectHandle, sessionid);
SetIdleConnectHandle(pConnectHandle);
return bRet;
}
//傳入空閑的句柄,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;
}
