MySQL由于它本身的小巧和操作的高效, 在数据库应用中越来越多的被采用.我在开发一个P2P应用的时候曾经使用MySQL来保存P2P节点,由于P2P的应用中,结点数动辄上万个,而且节点变化频繁,因此一定要保持查询和插入的高效.以下是我在使用过程中做的提高效率的三个有效的尝试.

使用statement进行绑定查询

使用statement可以提前构建查询语法树,在查询时不再需要构建语法树就直接查询.因此可以很好的提高查询的效率. 这个方法适合于查询条件固定但查询非常频繁的场合.

使用方法是:

•　　绑定, 创建一个MYSQL_STMT变量,与对应的查询字符串绑定,字符串中的问号代表要传入的变量,每个问号都必须指定一个变量.

•　　查询, 输入每个指定的变量, 传入MYSQL_STMT变量用可用的连接句柄执行.

代码如下:

//1.绑定

bool CDBManager::BindInsertStmt(MYSQL * connecthandle)

{

//作插入操作的绑定

MYSQL_BIND insertbind[FEILD_NUM];

if(m_stInsertParam == NULL)

m_stInsertParam = new CHostCacheTable;

m_stInsertStmt = mysql_stmt_init(connecthandle);

//构建绑定字符串

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结构数组, m_sInsertParam是这个statement关联的结构变量

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;

//绑定

if (mysql_stmt_bind_param(m_stInsertStmt, insertbind))

return false;

return true;

}

随机的获取记录

在某些数据库的应用中, 我们并不是要获取所有的满足条件的记录,而只是要随机挑选出满足条件的记录. 这种情况常见于数据业务的统计分析,从大容量数据库中获取小量的数据的场合.

有两种方法可以做到

1. 常规方法,首先查询出所有满足条件的记录,然后随机的挑选出部分记录.这种方法在满足条件的记录数很多时效果不理想.

2. 使用limit语法,先获取满足条件的记录条数, 然后在sql查询语句中加入limit来限制只查询满足要求的一段记录. 这种方法虽然要查询两次,但是在数据量大时反而比较高效.

示例代码如下:

//1.常规的方法

//性能瓶颈,10万条记录时,执行查询140ms, 获取结果集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) //检索

return 0;

//获取结果集

m_pResultSet = mysql_store_result(connecthandle);

if(!m_pResultSet) //获取结果集出错

return 0;

int iAllNumRows = (int)(mysql_num_rows(m_pResultSet)); ///

//计算待返回的结果数

int iReturnNumRows = (iAllNumRows <= RETURN_QUERY_HOST_NUM)? iAllNumRows:RETURN_QUERY_HOST_NUM;

if(iReturnNumRows <= RETURN_QUERY_HOST_NUM)

{

//获取逐条记录

for(int i = 0; i<>

{

//获取逐个字段

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

{

//随机的挑选指定条记录返回

int iRemainder = iAllNumRows%iReturnNumRows; ///

int iQuotient = iAllNumRows/iReturnNumRows; ///

int iStartIndex = rand()%(iRemainder + 1); ///

//获取逐条记录

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]);

}

}

//释放结果集内容

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)

{

//首先获取满足结果的记录条数,再使用limit随机选择指定条记录返回

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) //检索

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);

//计算待取记录的上下范围

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);

//计算待返回的结果数

int iReturnNumRows = (iAllNumRows <= RETURN_QUERY_HOST_NUM)?

iAllNumRows:RETURN_QUERY_HOST_NUM;