Cannot get Local Connection, No available resource, Wait-time expired

Question

Hi Friends,
Please answer my queries below.
Thanks and Regards
Busincess Requirement
I have to display a particular set of rows in a dashboard or screen, and it is being refreshed every 1 minute, also user can update from that screen displayed values.
The below program extracts some data from database and passes to the front end through a collection where it is being displayed.
Code Logic Flow
1. CockpitAction calls CockpitOraDAO for database results
2. CockpitOraDAO is a singleton class.
3. After getting the CockpitOraDAO object, the action will then call the getLabAreaCockpitDetails() method.
getLabAreaCockpitDetails will
     - Get the Connetion from the OracleConnectionManager class (It is a plain class with getPooledConnection() and releaseConnection() methods).
     - Execute the query and put the result to a collection
     - close the connection
     - return result to the calling action.
This getLabAreaCockpitDetails() are called around once in every 1 minute
So, I believe everytime a call is made to action for cockpit display, it will take the existing object of the CockpitOraDAO class and make a call to database. i.e there will be only one object of CockpitOraDAO reside in application server at any particular interval of time.
My Understandings
1. Only 1 object of CockpitOraDAO will reside in application server (provided it is not user longer and garbage collected) at a particular instance.
2. Many objects of Connection will be created and destroyed.(Each time the getLabAreaCockpitDetails() method is called, we will get one connection from connection pool and in finally the Connection will be released to connection pool).
My Problems
It is showing the "Cannot get Local Connection, No available resource, Wait-time expired"
after running around 1 full day.
My doubts
1. Can anybody say why I get this error ?
2. There may be some connections are not closed. But I have checked at finally block, the status of the connection is closed after calling this method.
3. There may be some problem due to the singleton instane of CockpitOraDAO, Is it affecting performance ?
4. Is it valid that I have to make CockpitOraDAO as Singleton ?
public class CockpitOraDAO extends DAOAdaptor //implements BISample
     private static CockpitOraDAO instance=null;
     private static boolean debug = true;
     * The below method will be used to provide the singleton intance of the CockpitOraDAO object.
     public static CockpitOraDAO getInstance()
          if (instance == null)
               synchronized (CockpitOraDAO.class)
                    if (instance == null)
                         instance = new CockpitOraDAO();
          return instance;
     * The below method will be used to get the cockpit details of the lab area.
     * This will return collecton of sample details for the specific lab.
     public Collection getLabAreaCockpitDetails(Collection prevCockpitDetailList,Collection filterCriteria) throws Exception
     if(debug)
          System.out.println("Inside CockpitOraDAO::getLabAreaCockpitDetails() method");
          Connection conn = null;
          boolean sampleExists = false;
          PreparedStatement pstmt=null;
          ResultSet rs=null;
          String returnStr=null;
          StringBuffer sqlQuery = null;
          String tempComment1=null, tempComment2=null;
          LabCockpitDO labc=null;
          LabCockpitDO labc2=null;
          Collection resultList=null, manCommentList=null, labCommentList=null, labCompCommentList=null;
          ArrayList result1List=null, prevCockpitDetail1List=null,filterList = null;
          OracleConnectionManager manager = null;
          boolean flag = false;
          try
               labc2 = new LabCockpitDO();
               prevCockpitDetail1List = (ArrayList) prevCockpitDetailList;
               sqlQuery = new StringBuffer();
               sqlQuery.append("select s.sample_sample_no sample_no, s.sample_inspection_lot_no inspection_lot_no,");
               manager = new OracleConnectionManager();
               conn = manager.getPooledConnection("myDS");
               pstmt = conn.prepareStatement(sqlQuery.toString());
               if(debug)
               System.out.println("Query********"+sqlQuery.toString());
               rs = pstmt.executeQuery();
          catch(Exception e)
               //System.out.println(e);
               throw e;
          finally
                    try
                         manager.releaseConnection("myDS");
if(debug)
System.out.println("Connection Status Closed=true/ Open=false=["+conn.isClosed()+"]");
if(conn!=null || !conn.isClosed())
conn.close();
if(debug)
System.out.println("Connection Status After Closing Connection Closed=true/ Open=false=["+conn.isClosed()+"]");
                         if(rs != null)
                              rs.close();
                         if(pstmt != null)
                              pstmt.close();
                         conn = null;
                         pstmt=null;
                         rs = null;
                         sqlQuery=null;
                         returnStr=null;
                         labc=null;
                         labc2=null;
                         manCommentList=null;
                         labCommentList=null;
                         labCompCommentList=null;
                         tempComment1=null;
                         tempComment2=null;
                         resultList=null;
                         prevCockpitDetailList=null;
                         prevCockpitDetail1List=null;
                    catch(Exception e)
                         //System.out.println("Unable to Release Connection ="+e);
                         throw e;
          //if(debug)     
          //System.out.println(resultList);
          return result1List;
     }

Answer 1

Hi,
As you can see from other posts, this is a very common problem. Until now the cause always ends up pointing to a connection not being close.
I suggest you try to run through a full single cycle of you app, while using the CLI monitoting to check that the connections created/closed matches the expected created/closed connections. Also that the number of free connections at the end is correct.