//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;
//使用limit作查询
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) //检索
return 0;
pResultSet = mysql_store_result(connecthandle);
if(!pResultSet)
return 0;
//获取逐条记录
for(int i = 0; i<iReturnNumRows; i++)
{
//获取逐个字段
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]);
}
//释放结果集内容
mysql_free_result(pResultSet);
return iReturnNumRows;
}
l 使用连接池管理连接.
在有大量节点访问的数据库设计中,经常要使用到连接池来管理所有的连接.
一般方法是:建立两个连接句柄队列,空闲的等待使用的队列和正在使用的队列.
当要查询时先从空闲队列中获取一个句柄,插入到正在使用的队列,再用这个句柄做数据库操作,完毕后一定要从使用队列中删除,再插入到空闲队列.
设计代码如下:
//定义句柄队列
typedef std::list<MYSQL *> CONNECTION_HANDLE_LIST;
typedef std::list<MYSQL *>::iterator CONNECTION_HANDLE_LIST_IT;
//连接数据库的参数结构
class CDBParameter
{
public:
char *host; ///<主机名
char *user; ///<用户名
char *password; ///<密码
char *database; ///<数据库名
unsigned int port; ///<端口，一般为0
const char *unix_socket; ///<套接字，一般为NULL
unsigned int client_flag; ///<一般为0
};
//创建两个队列
CONNECTION_HANDLE_LIST m_lsBusyList; ///<正在使用的连接句柄
CONNECTION_HANDLE_LIST m_lsIdleList; ///<未使用的连接句柄
//所有的连接句柄先连上数据库,加入到空闲队列中,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
{
//连接
for(int index = 0; index < CONNECTION_NUM; index++)
{
MYSQL * pConnectHandle = mysql_init((MYSQL*) 0); //初始化连接句柄
if(!mysql_real_connect(pConnectHandle, lpDBParam->host, lpDBParam->user, lpDBParam->password,\
lpDBParam->database,lpDBParam->port,lpDBParam->unix_socket,lpDBParam->client_fla))
return false;
//加入到空闲队列中
m_lsIdleList.push_back(pConnectHandle);
}
}
catch(...)
{
return false;
}
return true;
}
