error: PSQLException: FATAL: sorry, too many clients already

the error is:

aused by: org.hibernate.exception.GenericJDBCException: Cannot open connection
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:29)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:426)
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:119)
at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:57)
at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1326)
at org.hibernate.ejb.TransactionImpl.begin(TransactionImpl.java:38)
... 64 more
Caused by: org.postgresql.util.PSQLException: FATAL: sorry, too many clients already
at org.postgresql.core.v3.ConnectionFactoryImpl.readStartupMessages(ConnectionFactoryImpl.java:464)
at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:112)
at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:66)
at org.postgresql.jdbc2.AbstractJdbc2Connection.(AbstractJdbc2Connection.java:125)
at org.postgresql.jdbc3.AbstractJdbc3Connection.(AbstractJdbc3Connection.java:30)
at org.postgresql.jdbc3g.AbstractJdbc3gConnection.(AbstractJdbc3gConnection.java:22)
at org.postgresql.jdbc4.AbstractJdbc4Connection.(AbstractJdbc4Connection.java:30)
at org.postgresql.jdbc4.Jdbc4Connection.(Jdbc4Connection.java:24)
at org.postgresql.Driver.makeConnection(Driver.java:393)
at org.postgresql.Driver.connect(Driver.java:267)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:154)
at org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:110)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423)
... 69 more


see http://stackoverflow.com/questions/220374/do-i-have-to-close-every-entitymanager

a useful blog on web engineering

this blog and publications seems very related to my interest areas..
so note it down for later research:
http://marcobrambi.blogspot.com/

http://dbgroup.como.polimi.it/brambilla/pubs

Grid Computing vs Cloud Computing

an article comparing grid computing and cloud computing:
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=04738445

another link for the same article:
http://people.cs.uchicago.edu/~iraicu/publications/2008_GCE08_Clouds_Grids.pdf

logging in java apps

for starter, lets begin with java.util.logging..

http://www.java-tips.org/java-se-tips/java.util.logging/how-to-use-logger.html
http://www.rgagnon.com/javadetails/java-0501.html
http://www.roseindia.net/java/example/java/util/quintessential-logging-program.shtml

and log4j..
http://logging.apache.org/log4j/1.2/manual.html
http://www.basilv.com/psd/blog/2006/tips-for-using-log4j
http://homepage.mac.com/kelleherk/iblog/C1837526061/E2136921646/index.html

the interface:

package org.apache.log4j;

 public class Logger {

   // Creation & retrieval methods:
   public static Logger getRootLogger();
   public static Logger getLogger(String name);

   // printing methods:
   public void trace(Object message);
   public void debug(Object message);
   public void info(Object message);
   public void warn(Object message);
   public void error(Object message);
   public void fatal(Object message);

   // generic printing method:
   public void log(Level l, Object message);
}

adjust log level in glassfish