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• Searching for patterns to create a TCP Connection Pool for high performance messaging

  - by JoeGeeky

  I'm creating a new Client / Server application in C# and expect to have a fairly high rate of connections. That made me think of database connection pools which help mitigate the expense of creating and disposing connections between the client and database. I would like to create a similar capability for my application and haven't been able to find any good examples of how to apply this pattern. Do I really need to spin up an instance of a TcpClient every time I want to send a message to the server and receive a receipt message? Each connection is expected to transport between 1-5KB with each receiving a 1KB response message. I realize this question is somewhat vague, but I am starting from scratch so I am open to suggestions. Even if that means my suppositions are all wrong.

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• Is a base class with shared fields and functions good design

  - by eych

  I've got a BaseDataClass with shared fields and functions Protected Shared dbase as SqlDatabase Protected Shared dbCommand as DBCommand ... //also have a sync object used by the derived classes for Synclock'ing Protected Shared ReadOnly syncObj As Object = New Object() Protected Shared Sub Init() //initializes fields, sets connections Protected Shared Sub CleanAll() //closes connections, disposes, etc. I have several classes that derive from this base class. The derived classes have all Shared functions that can be called directly from the BLL with no instantiation. The functions in these derived classes call the base Init(), call their specific stored procs, call the base CleanAll() and then return the results. So if I have 5 derived classes with 10 functions each, totaling 50 possible function calls, since they are all Shared, the CLR only calls one at a time, right? All calls are queued to wait until each Shared function completes. Is there a better design with having Shared functions in your DAL and still have base class functions? Or since I have a base class, is it better to move towards instance methods within the DAL?

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• DataSource or ConnectionPoolDataSource for Application Server JDBC resources

  - by Vinnie

  When creating JNDI JDBC connection pools in an application server, I always specified the type as javax.sql.ConnectionPoolDataSource. I never really gave it too much thought as it always seemed natural to prefer pooled connections over non-pooled. However, in looking at some examples (specifically for Tomcat) I noticed that they specify javax.sql.DataSource. Further, it seems there are settings for maxIdle and maxWait giving the impression that these connections are pooled as well. Glassfish also allows these parameters regardless of the type of data source selected. Are javax.sql.DataSource pooled in an application server (or servlet container)? What (if any) advantages are there for choosing javax.sql.ConnectionPoolDataSource over javax.sql.DataSource (or vice versa)?

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• Cannot connect to sql server

  - by Tony

  Hi I cannot connect to Sql server remotely from management studio , It is corrrect User name and password, but how to enable remote connections to a sql server? what is other chances? Cannot connect to xxxx.xxxx.xxxx.xxxx =================================== A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (.Net SqlClient Data Provider) thanks

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• How to check connection leak using regular expression ?

  - by gauravkarnatak

  I have to check connection leak in my application i.e. open connections which have not been closed. After searching, after I found out that a thousands times connections have been opened but I can't manually go to each and every code fragment and check for connection close thing. I think, it could be possible using a regular expression but the fact is, I am not that well versed with regex that I could write one. Please suggest a regular expression for checking in a no of java files that a opened connection has been closed or not. My code pattern is something like this. try { /* Some code goes here */ con = EJBUtil.getConnection(JNDI_NAME); /* Some code goes here */ } finally { /* Some code goes here */ DBUtil.close(con); or closeConnection.close(con); /* Some code goes here */ }

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• An Actor "queue" ?

  - by synic

  In Java, to write a library that makes requests to a server, I usually implement some sort of dispatcher (not unlike the one found here in the Twitter4J library: http://github.com/yusuke/twitter4j/blob/master/twitter4j-core/src/main/java/twitter4j/internal/async/DispatcherImpl.java) to limit the number of connections, to perform asynchronous tasks, etc. The idea is that N number of threads are created. A "Task" is queued and all threads are notified, and one of the threads, when it's ready, will pop an item from the queue, do the work, and then return to a waiting state. If all the threads are busy working on a Task, then the Task is just queued, and the next available thread will take it. This keeps the max number of connections to N, and allows at most N Tasks to be operating at the same time. I'm wondering what kind of system I can create with Actors that will accomplish the same thing? Is there a way to have N number of Actors, and when a new message is ready, pass it off to an Actor to handle it - and if all Actors are busy, just queue the message?

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• PostgreSQL pgdb driver raises "can't rollback" exception

  - by David Parunakian

  Hello, for some reason I'm experiencing the Operational Error with "can't rollback" message when I attempt to roll back my transaction in the following context: try: cursors[instance].execute("lock revision, app, timeout IN SHARE MODE") cursors[instance].execute("insert into app (type, active, active_revision, contents, z) values ('session', true, %s, %s, 0) returning id", (cRevision, sessionId)) sAppId = cursors[instance].fetchone()[0] cursors[instance].execute("insert into revision (app_id, type) values (%s, 'active')", (sAppId,)) cursors[instance].execute("insert into timeout (app_id, last_seen) values (%s, now())", (sAppId,)) connections[instance].commit() except pgdb.DatabaseError, e: connections[instance].rollback() return "{status: 'error', errno:4, errmsg: \"%s\"}"%(str(e).replace('\"', '\\"').replace('\n', '\\n').replace('\r', '\\r')) The driver in use is PGDB. What is fundamentally wrong here?

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• can you use proxies to do load/stress testing on a server, with proxy serving as a sort of mirror?

  - by EndangeringSpecies

  suppose I want to test a server's and its web application's ability to handle many simultaneous connections well and show decent latency. So ideally I would want a thousand machines to bombard it with usage requests, but that's not practicable. So instead, can I just make a testing script with a thousand threads to run on the same server and have them perform the testing, connecting to the server via a geographically far-away proxy? My reasoning here is that the signal will have to travel realistically big distances to the proxy and back, so that sort of emulates the reality of real clients accessing the server. Then again, to take this one step further, are there prepackaged emulators/frameworks that could perform a similar test without using internet at all, just simulating the latency of the network, realistically creating all the socket connections and other resource intensive stuff etc?

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• Library Recommendation: C++ HTML Parser

  - by Zombies

  Preferably a light weight HTML parser, not exactly creating a browser or looking to modulate JS or any http connections.

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• More memory usage for IIS 6 asp.net 2.0 on webserver 2003

  - by Alan King

  Running a webserver 2003 SP2 (x86) with IIS 6 and asp.net 2. The box is running mostly dynamic asp pages connecting to a sql 2008 server. At any given time there is over 1 gig of memory available out of the 2 gig in the box. It seems like there would be a way for it to make better use of the free memory. It is using a default machine.config file and default http.sys. I would like to maximize incoming internet connections and database connections. Is there something I can do to make better use of the available memory?

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• Mixing .NET versions between website and virtual directories and the "server application unavailable" error Message

  - by Doug Chamberlain

  Backstory Last month our development team created a new asp.net 3.5 application to place out on our production website. Once we had the work completed, we requested from the group that manages are server to copy the app out to our production site, and configure the virtual directory as a new application. On 12/27/2010, two public 'Gineau Pigs' were selected to use the app, and it worked great. On 12/30/2010, We received notification by internal staff, that when that staff member tried to access the application (this was the Business Process Owner) they recieved the 'Server Application Unavailable' message. When I called the group that does our server support, I was told that it probably failed, because I didn't close the connections in my code. However, the same group went in and then created a separate app pool for this Extension Request application. It has had no issues since. I did a little googling, since I do not like being blamed for things. I found that the 'Server Application Unavailable' message will also appear when you have multiple applications using different frameworks and you do not put them in different application pools. Technical Details - Tree of our website structure Main Website <-- ASP Classic +-Virtual Directory(ExtensionRequest) <-- ASP 3.5 From our server support group: 'Reviewed server logs and website setup in IIS. Had to reset the application pool as it was not working properly. This corrected the website and it is now back online. We went ahead and created a application pool for the extension web so it is isolated from the main site pool. In the past we have seen other application do this when there is a connection being left open and the pool fills up. Would recommend reviewing site code to make sure no connections are being left open.' The Real Question: What really caused the failure? Isn't the connection being left open issue an ASP Classic issue? Wouldn't the ExtensionRequest application have to be used (more than twice) in the first place to have the connections left open? Is it more likely the failure is caused by them not bothering to setup the new Application in it's own App Pool in the first place? Sorry for the long windedness

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• Java DriverManager Always Assigns My Driver

  - by JGB146

  I am writing a driver to act as a wrapper around two separate MySQL connections (to distributed databases). Basically, the goal is to enable interaction with my driver for all applications instead of requiring the application to sort out which database holds the desired data. Most of the code for this is in place, but I'm having a problem in that when I attempt to create connections via the MySQL Driver, the DriverManager is returning an instance of my driver instead of the MySQL Driver. I'd appreciate any tips on what could be causing this and what could be done to fix it! Below is a few relevant snippets of code. I can provide more, but there's a lot, so I'd need to know what else you want to see. First, from MyDriver.java: public MyDriver() throws SQLException { DriverManager.registerDriver(this); } public Connection connect(String url, Properties info) throws SQLException { try { return new MyConnection(info); } catch (Exception e) { return null; } } public boolean acceptsURL(String url) throws SQLException { if (url.contains("jdbc:jgb://")) { return true; } return false; } It is my understanding that this acceptsURL function will dictate whether or not the DriverManager deems my driver a suitable fit for a given URL. Hence it should only be passing connections from my driver if the URL contains "jdbc:jgb://" right? Here's code from MyConnection.java: Connection c1 = null; Connection c2 = null; /** *Constructors */ public DDBSConnection (Properties info) throws SQLException, Exception { info.list(System.out); //included for testing Class.forName("com.mysql.jdbc.Driver").newInstance(); String url1 = "jdbc:mysql://server1.com/jgb"; String url2 = "jdbc:mysql://server2.com/jgb"; this.c1 = DriverManager.getConnection( url1, info.getProperty("username"), info.getProperty("password")); this.c2 = DriverManager.getConnection( url2, info.getProperty("username"), info.getProperty("password")); } And this tells me two things. First, the info.list() call confirms that the correct user and password are being sent. Second, because we enter an infinite loop, we see that the DriverManager is providing new instances of my connection as matches for the mysql URLs instead of the desired mysql driver/connection. FWIW, I have separately tested implementations that go straight to the mysql driver using this exact syntax (al beit only one at a time), and was able to successfully interact with each database individually from a test application outside of my driver.

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• Integrating WebSockets with Rails using Rack and Event Machine

  - by Toby Hede

  I have created an Asynchronous version of Rails 3 that I would like to integrate with a WebSocket implementation. I am using EventMachine, Ruby 1.9, Fibers and various em-flavoured libraries as documented by the wickedly good Ilya Grigorik. I have been looking at em-websocket as the handler for WebSocket connections but unsure of the best approach for hooking this into a Rails app. Ideally, this would work in a similar fashion to node.js with Express and Socket.io - incoming connections should be detected and dispatched to the WebSocket handler or the regular rails stack as indicated by the HTTP headers & etc. TL;DR WebSocket handler that plugs into an existing Rails application Transparently dispatch incoming WebSocket requests to endpoints in the app

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• Handling Incoming Data from Multiple Sockets in Python

  - by user859434

  Background: I have a current implementation that receives data from about 120 different socket connections in python. In my current implementation, I handle each of these separate socket connections with a dedicated thread for each. Each of these threads parse the data and eventually store it within a shared locked dictionary. These sockets DO NOT have uniform data rates, some sockets get more data than others. Question: Is this the best way to handle incoming data in python, or does python have a better way on handling multiple sockets per thread?

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• Oracle data provider hangs IIS worker process when web site is stopped

  - by Greg

  We're experiencing a nasty issue in Oracle 11g Release 2 where the w3wp process takes over and entire processor core, and debugging shows that the Oracle data provider is throwing ThreadAbortExceptions infinitely. A developer found this issue by doing the following: 1) Browse a web site that uses Oracle data connections locally (http://localhost/OracleWebSite) - we use IIS, not the ASP.NET dev server, for all of our sites. This ensures that the w3wp process is running and that an active Oracle pool of connections exists in the app pool. 2) Stop the web site (or perform a Rebuild All operation in Visual Studio on the web site in question). Our Oracle connection handling in the affected applications (all Oracle web apps) is well-established and robust. This issue does not occur if we disable connection pooling. This issue does not occur in Oracle 11g Release 1.

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• Terminate an inactive socket connection from TIdTCPServer

  - by A.J.

  We have an application which listens for incoming TCP requests using the Indy 10.1.1 components that ship with Delphi 2007. Occassionally we receive incoming connections which are not from our client application. Typically, one of two things happens: 1) the connection is terminated by the client before any data is received, or 2) data is received which we're not expecting and we manually terminate the connection. However, we've received connections where no data is received and appear to persist until the client terminates the connection from their end. Is there a way to terminate such a connection from the server if no data is received after a specified amount of time?

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• MongoDB db.serverStatus() gives error when running using tunnel that is targetted to api.cloudfoundry.com

  - by Ajay

  Following is the console session... C:\Users\xxx>vmc tunnel myMongoDB Getting tunnel connection info: OK Service connection info: username : uuuu password : pppp name : db url : mongodb://uuuu:[email protected]:25200/db Starting tunnel to myMongoDB on port 10000. 1: none 2: mongo 3: mongodump 4: mongorestore Which client would you like to start?: 2 Launching 'mongo --host localhost --port 10000 -u uuuu -p pppp db' MongoDB shell version: 2.0.6 connecting to: localhost:10000/db > db.serverStatus() { "errmsg" : "need to login", "ok" : 0 } > Which credentials should I use to login (assuming should use db.auth) to get rid of the error "{ "errmsg" : "need to login", "ok" : 0 }". When I run the same in micro CF on my machine it works ok and gives me the expected output. P.S. I'm trying this to get to know the current connections on my application, written in node.js. Trying to debug some issues with connections to the DB. If there is any other alternative that I can use please suggest that as well.

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• Is passing a Command object/Reader to a function a good idea?

  - by Cyril Gupta

  I've been getting some inexplicable errors (running out of connections from the connection pool) with MySql database with .Net 4 (C#). Till now all my attempts at finding a reason for this have been in vain. Now I also have a situation in which a lock on a table is not cleared for a long time even though all I have been doing is read operations from it. My code looks okay (I've put all readers and connections in using blocks). The only anomaly I have is that I've been passing MySqlCommand and MySqlDataReader objects as parameters to functions who work with them. That doesn't seem like a bad idea for me because it avoids some repetition (DRY!). But since I can't find any other explanation I have to suspect that this is causing the problem. What do you think?

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• TcpListener problem - re-binding to same port with different local addresses

  - by Zvika

  I'm trying to do the following: listen on some port for loopback connections only, and then start listening on any IP address. Here is the code: TcpListener l1 = new TcpListener(new IPEndPoint(IPAddress.Loopback, 12345)); l1.Start(); Socket s = l1.AcceptSocket(); Console.ReadKey(); //s.Close(); l1.Stop(); TcpListener l2 = new TcpListener(new IPEndPoint(IPAddress.Any, 12345)); l2.Start(); l2.AcceptSocket(); Console.ReadKey(); The problem is that if a client connects while listening on the Loopback address (l1), then no other client can connect to the Loopback address when the second listener (l2) starts listening. why is that? Another thing I noticed is that if I close all clients that connected to l1 (the remarked line), then l2 does accept loopback connections. Any ideas?

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• How can I implement "real time" messaging on Google AppEngine?

  - by Freed

  I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine. Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting. Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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• MySQL with Java: Open connection only if possible

  - by emempe

  I'm running a database-heavy Java application on a cluster, using Connector/J 5.1.14. Therefore, I have up to 150 concurrent tasks accessing the same MySQL database. I get the following error: Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Too many connections This happens because the server can't handle so many connections. I can't change anything on the database server. So my question is: Can I check if a connection is possible BEFORE I actually connect to the database? Something like this (pseudo code): check database for open connection slots if (slot is free) { Connection cn = DriverManager.getConnection(url, username, password); } else { wait ... } Cheers

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• vb.net : is it possible to connect to sql server 2008 via odbc but not through vb.net code?

  - by phill

  I'm supporting an old vb.net program whose database it connected to was moved from SQL Server 2005 to SQL Server 2008. Is there a setting on SQL Server 2008 which will allow ODBC connections to access the database but not allow VB.NET to connect to it programmatically? the error i keep receiving in the app is: An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 – Could not open a connection to SQL Server) however I can connect to it when I create a system dsn to the sql server instance and through VS2005's Tools Connect to Database. Here is the code I'm using to connect: dim strC as string strC = "data source=bob; database=subscribers; user id=bobuser; password=passme" dim connection as New SqlClient.SqlConnection(strC) try connection.open() catch ex as Exception msgbox(ex.message) end try connection.Close()

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• How to tell iPhone NSURLConnection to abort

  - by Jahmic

  I have an app that makes moderate use of NSURLConnection. These async calls eventually finish and release properly (it looks like), but sometimes it takes some time for them to finish. So, there are times when I exit the app, (note, not just sending it the background), that some of these connections are still active. If I immediately restart the app, the app freezes on startup. (didFinishLaunchingWithOptions never seems to get called). While I'm not certain these connections are the issue, it would probably be good to terminate or cancel any remaining. Any suggestions on how to do this? Bonus points on how to debug the restart also. (I'm already saving NSLog statements to a downloadable file)

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• Best way to handle enable/disable of UIButtons on iPhone

  - by Anonymous

  I have an increase button and a decrease button, both of which affect a variable. The variable has a minimum and the decrease button will be disabled once that minimum is reached. Likewise for the maximum value of the variable. In my controller, I have two IBActions for both the increase and decrease actions, and two IBOutlets, in order to disable the buttons accordingly. At the bottom of my KVO statement to handle the value change, I have: increaseButton.enabled = value != MAX; decreaseButton.enabled = value != MIN; While this code is functional, I can't help but feel that feel this is a naive approach to the problem, especially since this requires 4 connections. Is there a better solution to this, one that uses fewer connections?

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• How to figure out why ssh session does not exit sometimes?

  - by WilliamKF

  I have a C++ application that uses ssh to summon a connection to the server. I find that sometimes the ssh session is left lying around long after the command to summon the server has exited. Looking at the Centos4 man page for ssh I see the following: The session terminates when the command or shell on the remote machine exits and all X11 and TCP/IP connections have been closed. The exit status of the remote program is returned as the exit status of ssh. I see that the command has exited, so I imagine not all the X11 and TCP/IP connections have been closed. How can I figure out which of these ssh is waiting for so that I can fix my summon command's C++ application to clean up whatever is being left behind that keeps the ssh open. I wonder why this failure only occurs some of the time and not on every invocation? It seems to occur approximately 50% of the time. What could my C++ application be leaving around to trigger this?

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