我要评论//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;
}
//提取一个空闲句柄供使用
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 //特殊情况,闲队列中为空,返回为空
{
pconnecthandle = 0;
}
m_listmutex.release();
return pconnecthandle;
}
//从使用队列中释放一个使用完毕的句柄,插入到空闲队列
void cdbmanager::setidleconnecthandle(mysql * connecthandle)
{
m_listmutex.acquire();
m_lsbusylist.remove(connecthandle);
m_lsidlelist.push_back(connecthandle);
m_listmutex.release();
}
//使用示例,首先获取空闲句柄,利用这个句柄做真正的操作,然后再插回到空闲队列
bool cdbmanager::deletehostcachebysessionid(char * sessionid)
{
mysql * pconnecthandle = getidleconnecthandle();
if(!pconnecthandle)
return 0;
bool bret = deletehostcachebysessionid(pconnecthandle, sessionid);
setidleconnecthandle(pconnecthandle);
return bret;
}
//传入空闲的句柄,做真正的删除操作
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) //删除
return false;
return true;
}
2
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