[ mongoDB ] - MongoDB 连接池
本文内容纲要：
一.mongoDB中的连接池
刚上手MongoDB，在做应用时，受以前使用关系型数据库的影响，会考虑数据库连接池的问题！
关系型数据库中，我们做连接池无非就是事先建立好N个连接（connection），并构建成一个连接池（connectionpool），提供去连接和归还连接等操作。
而在MongoDB中，我们先来看看怎么进行操作，以insert为例：
Mongom=newMongo("localhost",27017);
DBdb=m.getDB("mydb");
//getcollection
DBCollectioncoll=db.getCollection("testCollection")
//insert
BasicDBObjectdoc=newBasicDBObject();
...
coll.insert(doc);
[伪代码]
如果套用以前的经验，可能会想偏，引用官方文档的一句话可能会豁然开朗。
Note:TheMongoobjectinstanceactuallyrepresentsapoolofconnectionstothedatabase;youwillonlyneedoneobjectofclassMongoevenwithmultiplethreads.Seetheconcurrencydocpageformoreinformation.
TheMongoclassisdesignedtobethreadsafeandsharedamongthreads.Typicallyyoucreateonly1instanceforagivenDBclusteranduseitacrossyourapp.Ifforsomereasonyoudecidetocreatemanymongointances,notethat:
- allresourceusagelimits(maxconnections,etc)applypermongoinstance
- todisposeofaninstance,makesureyoucallmongo.close()tocleanupresources
mongo实例其实已经是一个现成的连接池了，而且线程安全。这个内置的连接池默认初始了10个连接，每一个操作（增删改查等）都会获取一个连接，执行操作后释放连接。
二.连接池的重要参数
内置连接池有多个重要参数，分别是：
- connectionsPerHost：每个主机的连接数
- threadsAllowedToBlockForConnectionMultiplier：线程队列数，它以上面connectionsPerHost值相乘的结果就是线程队列最大值。如果连接线程排满了队列就会抛出“Outofsemaphorestogetdb”错误。
- maxWaitTime:最大等待连接的线程阻塞时间
- connectTimeout：连接超时的毫秒。0是默认和无限
- socketTimeout：socket超时。0是默认和无限
- autoConnectRetry：这个控制是否在一个连接时，系统会自动重试
其设置方式如下：
MongoOptionsopt=mongo.getMongoOptions();
opt.connectionsPerHost=10;//poolsize
opt.threadsAllowedToBlockForConnectionMultiplier=10;
//其他参数类似
详情参考mongoDBAPI：
boolean
autoConnectRetry Iftrue,thedriverwillkeeptryingtoconnecttothesameserverincasethatthesocketcannotbeestablished.
int
connectionsPerHost ThemaximumnumberofconnectionsallowedperhostforthisMongoinstance.
int
connectTimeout Theconnectiontimeoutinmilliseconds.
DBDecoderFactory
dbDecoderFactory OverridetheDBCallbackfactory.
DBEncoderFactory
dbEncoderFactory Overridetheencodingfactory.
String
description Thedescriptionfor
Mongo instancescreatedwiththeseoptions. boolean
fsync The"fsync"valueoftheglobalWriteConcern.
boolean
j The"j"valueoftheglobalWriteConcern.
long
maxAutoConnectRetryTime ThemaximumamountoftimeinMStospendretryingtoopenconnectiontothesameserver.
int
maxWaitTime Themaximumwaittimeinmsthatathreadmaywaitforaconnectiontobecomeavailable.
boolean
safe If true thedriverwilluseaWriteConcernofWriteConcern.SAFEforalloperations.
boolean
slaveOk Deprecated. ReplacedinMongoDB2.0/JavaDriver2.7withReadPreference.SECONDARY
SocketFactory
socketFactory setsthesocketfactoryforcreatingsocketstomongodDefaultisSocketFactory.getDefault()
boolean
socketKeepAlive Thisflagcontrolsthesocketkeepalivefeaturethatkeepsaconnectionalivethroughfirewalls
Socket.setKeepAlive(boolean) Defaultisfalse. int
socketTimeout ThesockettimeoutinmillisecondsItisusedforI/Osocketreadandwriteoperations
Socket.setSoTimeout(int) Defaultis0andmeansnotimeout. int
threadsAllowedToBlockForConnectionMultiplier thismultiplier,multipliedwiththeconnectionsPerHostsetting,givesthemaximumnumberofthreadsthatmaybewaitingforaconnectiontobecomeavailablefromthepool.
int
w The"w"valueoftheglobalWriteConcern.
int
wtimeout The"wtimeout"valueoftheglobalWriteConcern.
三.连接池实践
packagecom.bts.dao.mongodb;
importjava.net.UnknownHostException;
importcom.bts.util.ConfTool;
importcom.mongodb.DB;
importcom.mongodb.Mongo;
importcom.mongodb.MongoException;
importcom.mongodb.MongoOptions;
/**
*@authorhuangfox
*@data2012-4-1
*@emailhuangfox009@126.com
*@desc
*/
publicclassMongoManager{
privatestaticMongomongo=null;
privateMongoManager(){
}
/**
*根据名称获取DB，相当于是连接
*
*@paramdbName
*@return
*/
publicstaticDBgetDB(StringdbName){
if(mongo==null){
//初始化
init();
}
returnmongo.getDB(dbName);
}
/**
*初始化连接池，设置参数。
*/
privatestaticvoidinit(){
StringconfFilePath="";
ConfToolconf=newConfTool(confFilePath);
Stringhost=conf.getValue("host");//主机名
intport=newInteger(conf.getValue("port"));//端口
intpoolSize=newInteger(conf.getValue("poolSize"));//连接数量
intblockSize=newInteger(conf.getValue("blockSize"));//等待队列长度
//其他参数根据实际情况进行添加
try{
mongo=newMongo(host,port);
MongoOptionsopt=mongo.getMongoOptions();
opt.connectionsPerHost=poolSize;
opt.threadsAllowedToBlockForConnectionMultiplier=blockSize;
}catch(UnknownHostExceptione){
//logerror
}catch(MongoExceptione){
//logerror
}
}
}
本文内容总结：
原文链接：https://www.cnblogs.com/huangfox/archive/2012/04/01/2428947.html