connection interview questions
Top connection frequently asked interview questions
My PHP/MS Sql Server 2005/win 2003 Application occasionally becomes very unresponsive, the memory/cpu usage does not spike. If i try to open any new connection from sql management studio, then the it just hangs at the open connection dialog box.
how to deterime the total number of active connections ms sql server 2005
Source: (StackOverflow)
In my Python socket program, I sometimes need to interrupt it with ctrl-c. When I do this, it does close the connection using socket.close() however when I try to reopen it I have to wait what seems like a minute before I can connect again. How does one correctly close a socket? Or is this intended?
Source: (StackOverflow)
Sometimes I get Oracle connection problems because I can't figure out which tnsnames.ora file my database client is using.
What's the best way to figure this out? ++happy for various platform solutions.
Source: (StackOverflow)
3 questions:
What is the difference between connection and read timeout for sockets?
What does connection timeout set to "infinity" mean? In what situation can it remain in an infinitive loop? and what can trigger that the infinity-loop dies?
What does read timeout set to "infinity" mean? In what situation can it remain in an infinitive loop? and what can trigger that the infinity-loop dies?
Source: (StackOverflow)
I understand the basics of how ports work. However, what I don't get is how multiple clients can simultaneously connect to say port 80. I know each client has a unique (for their machine) port. Does the server reply back from an available port to the client, and simply state the reply came from 80? How does this work?
Source: (StackOverflow)
I've had a bug in our software that occurs when I receive a connection timeout. These errors are very rare (usually when my connection gets dropped by our internal network). How can I generate this kind of effect artificially so I can test our software?
If it matters the app is written in C++/MFC using CAsyncSocket classes.
Edit:
I've tried using a non-existant host, and I get the socket error:
WSAEINVAL (10022) Invalid argument
My next attempt was to use Alexander's suggestion of connecting to a different port, e.g. 81 (on my own server though). That worked great. Exactly the same as a dropped connection (60 second wait, then error). Thank you!
Source: (StackOverflow)
I have many users on my web site (20000-60000 per day), which is a download site for mobile files. I have remote access to my server (windows server 2008-R2). I've received "Server is unavailable" errors before, but am now seeing a connection timeout error. I'm not familiar with this - why does it occur and how can I fix it?
The full error is below:
Server Error in '/' Application. Timeout expired. The timeout period
elapsed prior to completion of the operation or the server is not
responding. The statement has been terminated. Description: An
unhandled exception occurred during the execution of the current web
request. Please review the stack trace for more information about the
error and where it originated in the code.
Exception Details: System.Data.SqlClient.SqlException: Timeout
expired. The timeout period elapsed prior to completion of the
operation or the server is not responding. The statement has been
terminated.
Source Error:
An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of
the exception can be identified using the exception stack trace below.
Stack Trace:
[SqlException (0x80131904): Timeout expired. The timeout period
elapsed prior to completion of the operation or the server is not
responding. The statement has been terminated.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception,
Boolean breakConnection) +404
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning() +412
System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior,
SqlCommand cmdHandler, SqlDataReader dataStream,
BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject
stateObj) +1363
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds,
RunBehavior runBehavior, String resetOptionsString) +6387741
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior
cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean
async) +6389442
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior
cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String
method, DbAsyncResult result) +538
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult
result, String methodName, Boolean sendToPipe) +689
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +327
NovinMedia.Data.DbObject.RunProcedure(String storedProcName,
IDataParameter[] parameters, Int32& rowsAffected) +209
DataLayer.OnlineUsers.Update_SessionEnd_And_Online(Object Session_End,
Boolean Online) +440
NiceFileExplorer.Global.Application_Start(Object sender, EventArgs e)
+163
[HttpException (0x80004005): Timeout expired. The timeout period
elapsed prior to completion of the operation or the server is not
responding. The statement has been terminated.]
System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext
context, HttpApplication app) +4052053
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr
appContext, HttpContext context, MethodInfo[] handlers) +191
System.Web.HttpApplication.InitSpecial(HttpApplicationState state,
MethodInfo[] handlers, IntPtr appContext, HttpContext context) +352
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr
appContext, HttpContext context) +407
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr
appContext) +375
[HttpException (0x80004005): Timeout expired. The timeout period
elapsed prior to completion of the operation or the server is not
responding. The statement has been terminated.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11686928
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context)
+141 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest
wr, HttpContext context) +4863749
EDIT AFTER ANSWERS:
my Application_Start
in Global.asax
is like below:
protected void Application_Start(object sender, EventArgs e)
{
Application["OnlineUsers"] = 0;
OnlineUsers.Update_SessionEnd_And_Online(
DateTime.Now,
false);
AddTask("DoStuff", 10);
}
The stored procedure being called is:
ALTER Procedure [dbo].[sp_OnlineUsers_Update_SessionEnd_And_Online]
@Session_End datetime,
@Online bit
As
Begin
Update OnlineUsers
SET
[Session_End] = @Session_End,
[Online] = @Online
End
I have two methods for getting online users:
- using
Application["OnlineUsers"] = 0;
- the other one using database
So, for method #2 I reset all OnlineUsers at Application_Start
. There are over 482,751 records in that table.
Source: (StackOverflow)
I have installed PostgreSQL 8.4 on my CentOS server and connected to root user from shell and accessing the PostgreSQL shell.
I created the database and user in PostgreSQL.
While trying to connect from my PHP script it shows me authentication failed.
How do I create a new user and how to grant permissions to them for a particular DB?
Source: (StackOverflow)
If I do SHOW GRANTS
in my mysql database I get
GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost'
IDENTIFIED BY PASSWORD 'some_characters'
WITH GRANT OPTION
If I am not mistaken, root@localhost
means that user root
can access the server only from localhost
. How do I tell MySQL to grant root
the permission to access this mysql server from every other machine (in the same network), too?
Source: (StackOverflow)
In a Linux environment, I need to detect the physical connected or disconnected state of an RJ45 connector to its socket. Preferably using BASH scripting only.
The following solutions which have been proposed on other sites do NOT work for this purpose:
- Using 'ifconfig' - since a network cable may be connected but the network not properly configured or not currently up.
- Ping a host - since the product will be within a LAN using an unknown network configuration and unknown hosts.
Isn't there some state which can be used in the /proc file system (everything else is in there)?
How is the Linux world suppose to have their own version of the Windows bubble that pop up from the icon tray indicating that you've just unplugged the network cable?
Kent Fredric and lothar, both of your answers satisfy my need... thanks a lot! Which one I'll use... I still don't know.
I guess I can't put you both down as the correct answer? And its probably fair for you that I do choose one. Flip a coin I guess? Again, thanks!
Source: (StackOverflow)
Those "fine" RFCs mandate from every RFC-client that they beware of not using more than 2 connections per host...
Microsoft implemented this in WebClient. I know that it can be turned off with
App.config:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.net>
<connectionManagement>
<add address="*" maxconnection="100" />
</connectionManagement>
</system.net>
</configuration>
(found on http://social.msdn.microsoft.com/forums/en-US/netfxnetcom/thread/1f863f20-09f9-49a5-8eee-17a89b591007 )
But how can I do it programmatically?
Accordin to
http://msdn.microsoft.com/en-us/library/system.net.servicepointmanager.defaultconnectionlimit.aspx
"Changing the DefaultConnectionLimit property has no effect on existing
ServicePoint objects; it affects only ServicePoint objects that are
initialized after the change. If the value of this property has not been
set either directly or through configuration, the value defaults to the
constant DefaultPersistentConnectionLimit."
I'd like best to configure the limit when I instanciate the WebClient, but just removing this sad limitation programmatically at the start of my programm would be fine, too.
The server I access is not a regular webserver in the internet, but under my control and in the local lan. I want to do API-calls, but I don't use webservices or remoting
Source: (StackOverflow)
I am getting the following error trying to read from a socket. I'm doing a readInt()
on that InputStream
, and I am getting this error. Perusing the documentation this suggests that the client part of the connection closed the connection. In this scenario, I am the server.
I have access to the client log files and it is not closing the connection, and in fact its log files suggest I am closing the connection. So does anybody have an idea why this is happening? What else to check for? Does this arise when there are local resources that are perhaps reaching thresholds?
I do note that I have the following line:
socket.setSoTimeout(10000);
just prior to the readInt()
. There is a reason for this (long story), but just curious, are there circumstances under which this might lead to the indicated error? I have the server running in my IDE, and I happened to leave my IDE stuck on a breakpoint, and I then noticed the exact same errors begin appearing in my own logs in my IDE.
Anyway, just mentioning it, hopefully not a red herring. :-(
Source: (StackOverflow)
I have a loop over a bunch of URLs, for each one I'm doing the following:
private String doQuery(String url) {
HttpGet httpGet = new HttpGet(url);
setDefaultHeaders(httpGet); // static method
HttpResponse response = httpClient.execute(httpGet); // httpClient instantiated in constructor
int rc = response.getStatusLine().getStatusCode();
if (rc != 200) {
// some stuff...
return;
}
HttpEntity entity = response.getEntity();
if (entity == null) {
// some stuff...
return;
}
// process the entity, get input stream etc
}
The first query is fine, the second throws this exception:
Exception in thread "main"
java.lang.IllegalStateException:
Invalid use of
SingleClientConnManager: connection
still allocated. Make sure to release
the connection before allocating
another one. at
org.apache.http.impl.conn.SingleClientConnManager.getConnection(SingleClientConnManager.java:199)
at
org.apache.http.impl.conn.SingleClientConnManager$1.getConnection(SingleClientConnManager.java:173)......
This is just a simple single-threaded app. How can I release this connection?
Source: (StackOverflow)
When updating from subversion repository using tortoise svn client I get error looking like that:
Could not read chunk size: An existing connection was forcibly closed by the remote host.
It doesn't prevent me from updating, just interrupts update process, so that I have to repeat update several times, before it is complete.
What can cause such behaviour and how to fix it?
Source: (StackOverflow)
When does java let go of a connections to a URL? I don't see a close() method on either URL or URLConnection so does it free up the connection as soon as the request finishes? I'm mainly asking to see if I need to do any clean up in an exception handler.
try {
URL url = new URL("http://foo.bar");
URLConnection conn = url.openConnection();
// use the connection
}
catch (Exception e) {
// any clean up here?
}
Source: (StackOverflow)