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:
//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;
}
l 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:
//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;
}
l 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:
//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;
}
