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.
l 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;
}
//2.查询
bool cdbmanager::inserthostcache2(mysql * connecthandle, char * sessionid, char * channelid, int isptype, /
unsigned int eip, unsigned short eport, unsigned int iip, unsigned short iport)
{
//填充结构变量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;
//执行statement,性能瓶颈处
if(mysql_stmt_execute(m_stinsertstmt))
return false;
return true;
}
l 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)); ///<所有的搜索结果数
//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<ireturnnumrows; 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; ///<余数
int iquotient = iallnumrows/ireturnnumrows; ///<商
int istartindex = rand()%(iremainder + 1); ///<开始下标
//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;
//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;
}
