提高MySQL 查询效率的三个技巧

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;

}

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