// 先针对参数有效性进行检查　　// ......

　　// 判断是不是上一个认证请求还没做完　　// First check whether this is a repeat attempt from a recent pending// login before attempting to decrypt and log in.if (this->handleResentPendingAttempt( source, header.replyID )){// ignore this one, it's in progress
        loginStats_.incPending();return;}// 判断是否是否了加密
#ifdef USE_OPENSSLMercury::PublicKeyCipher * pPrivateKey = &privateKey_;
#elseMercury::PublicKeyCipher * pPrivateKey = NULL;
#endif//.......
　　// 判断是否之前有认证cache// First check whether this is a repeat attempt from a recent// resolved login before attempting to log in.if (this->handleResentCachedAttempt( source, pParams, header.replyID )){// ignore this one, we've seen it recentlyreturn;}// ......INFO_MSG( "Logging in %s{%s} (%s)\n",pParams->username().c_str(),pParams->password().c_str(),source.c_str() );// Remember that this attempt is now in progress and discard further// attempts from that address for some time after it completes.
    cachedLoginMap_[ source ].reset();cachedLoginMap_[ source ].pParams( pParams );DatabaseReplyHandler * pDBHandler =new DatabaseReplyHandler( source, header.replyID, pParams );　　　　// 发送给DBMgrMercury::Bundle    & dbBundle = this->dbMgr().bundle();dbBundle.startRequest( DBInterface::logOn, pDBHandler );dbBundle << source << false /*off channel*/ << *pParams;this->dbMgr().send();

void * /*arg*/ )
{uint8 status;data >> status;　　// 检查认证返回码if (status != LogOnStatus::LOGGED_ON){　　　　// 如果认证失败        　　　　// ......}LoginReplyRecord lrr;data >> lrr;// If the client has an external address, send them the firewall// address instead!if (!LoginApp::instance().netMask().containsAddress( clientAddr_.ip )){INFO_MSG( "DatabaseReplyHandler::handleMessage: ""Redirecting external client %s to firewall.\n",clientAddr_.c_str() );lrr.serverAddr.ip = LoginApp::instance().externalIP(); }
　　　　// 返回client认证结果，并且缓存认证结果    　　LoginApp::instance().sendAndCacheSuccess( clientAddr_, replyID_, lrr, pParams_ );gNumLogins++;delete this;
}

In terms of load, a single LoginApp should be sufficient for most purposes. However, as this is still a potential bottleneck, and single point of failure, BigWorld supports running multiple LoginApps.
The remaining issue then is how to distribute the client login requests across multiple login servers. The standard way to do this is use a DNS solution similar to how popular web sites balance traffic load across  multiple machines.