I have a C# Console Application that is essentially a long batch process that processes data on a nightly basis across many different databases. What is the proper or preferred way to test basic database connectivity at the beginning of this type of program? I ran into the issue of having an expired database password for one of my connections that was caught by exception handling but I want to test for basic connectivity at the very beginning.
Would a simple SELECT query suffice or is there a more efficient way of doing this for numerous databases?
IMHO the simplest way is trying to connect to database and, if you have a failure, you give up.
As you're running a night batch, it's not important to understand immediately the reason and solve it.
So something like this
using(SqlConnection conn = new SqlConnection(connectionString))
{
try
{
conn.Open();
// Do what you please here
}
catch (Exception ex)
{
// Write error to file
File.Append(...,
DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss") + " " +
ex.Message);
}
finally
{
conn.Close();
}
}
Next morning you can check file for errors...
'Connection.open`
is the simple way to determine if you can connect to db or not.
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
}
If you get a SqlException with number 18487 or 18488 it indicates the password has been changed.
Connection.changePassword
You don't need to run any query.
If you use SqlConnection passing the connection string, you can just try to Open() the connection and you'll get an exception if you cannot connect
Something like:
try
{
var cnn = new SqlConnection(connectionString);
cnn.Open();
}
catch
{
// connection failed, do something
}
Opening (and then closing) a connection should be sufficient to test the password. however, this does not tell you , if a db-user has permissions to access specific tables.
Related
I have a webservice running on IIS, which contains the class to connect to the SQL server. Most of the time, we are able to connect the SQL server using the below code. But some time we could not connect the sql server. We are not getting any error. Here is the source code:
public SqlConnection DbConnectSql()
{
string str = "Server=xxxx\xxx;database=production;Timeout=60000;user id=sa;password=888*;";
_con = new SqlConnection(str);
if (_con.State == ConnectionState.Open)
_con.Close();
_con.Open();
return _con;
}
We are not getting any response during the execution of _con.Open();. We could not understand why we are not getting any response. I have to restart the IIS every 2 days to open the SQL connection. Can anyone let me know the why I have to restart the IIS to work _con.Open(); method?
Here's an interleaving of two calls to DbConnectSql that will a) end up with two threads sharing use of one connection object and b) leaks an open connection object:
//Thread 1
public SqlConnection DbConnectSql()
{
string str = ...;
_con = new SqlConnection(str);
if (_con.State == ConnectionState.Open)
_con.Close();
_con.Open();
//Thread 2
public SqlConnection DbConnectSql()
{
string str = ...;
//-->Look, thread 2 is overwriting _con-->
_con = new SqlConnection(str);
return _con;
}
if (_con.State == ConnectionState.Open)
_con.Close();
_con.Open();
return _con;
}
If we're lucky, then the first caller won't try to use the connection object before the second caller gets around to calling Open on it1. But the connection created by the first caller has been opened and now nobody has a reference to it.
You'll be getting errors because the connection pool (eventually) becomes exhausted and so the Open call will throw an exception. Why you don't see the exception isn't diagnosable from the code shown.
You're probably being lucky to last 2 days at a time, because these connections are eligible for garbage collection and so will eventually be returned to the connection pool.
Far better to just share the connection string around. Construct SqlConnection (and SqlCommand) objects in using statements that keep them nicely locally scoped and ensures that they are cleaned up neatly. You don't need this DbConnectSql function. It's doing more harm than good.
1And there are likely to be other possible errors here, if one caller tries to retrieve a result set whilst the other caller is still retrieving one.
I have a .Net application that is creating a new database. The current code is working great in development environment and in many production environments. So I am confident the code is fine.
However, we have a specific instance where the user is getting a timeout while the application is running the following SQL Command:
CREATE DATABASE NameOfDatabase
The code is pretty simple, and as you can see it uses the default timeout period for SQL commands which is 30 seconds:
using (SqlConnection connection = new SqlConnection(connectionString))
{
string query = "CREATE DATABASE " + databaseName;
SqlCommand command = new SqlCommand(query, connection);
connection.Open();
command.ExecuteNonQuery();
}
Note: our log file shows the error occurs on ExecuteNonQuery which suggests that this is NOT a timeout while opening the connection, and rather during query execution.
The specific .Net error is:
Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
With a line from the stack trace to show my reasoning on it being a command timeout (not a connection timeout):
at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
Note: This error information is obtained using a try/catch around the code which was left out of the question for simplicity as it is not relevant to the problem.
Questions
Under any reasonable (or even uncommon) situations, should a CREATE DATABASE query take this long to run and still be successful?
If it shouldn't take that long, what are the common causes for a timeout? (where should I be looking to debug the problem?)
I do not have enough rep points to comment. To get the specific error wrap command.ExecuteNonQuery(); in a try catch. at least you can get the specific error that is occurring. Also use using with SqlCommand that will dispose that object. Connection State
using (SqlConnection connection = new SqlConnection(connectionString))
{
string query = "CREATE DATABASE " + databaseName;
using(SqlCommand command = new SqlCommand(query, connection))
{
try
{
connection.Open();
if (connection.State == ConnectionState.Open)
command.ExecuteNonQuery();
}
catch(Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
}
}
Maybe this TechNet article can help? Troubleshooting: Timeout Expired
I would like to detect connection state to MySql database. My database is deployed in different server than my app and there is good chances to lose connection to it via network. So I have to take this scenario into consideration.
Here is what I tried so far (a simplified test example):
static string connectionString = "***";
public static MySqlConnection Connection;
static System.Timers.Timer _timer;
static void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
try
{
if (Connection.State != System.Data.ConnectionState.Open)
Connection.Open();
// Call method to invoke MySqlCommand.ExecuteNonQuery
mysqlCommand.ExecuteNonQuery();
}
catch (MySqlException ex)
{
Console.WriteLine("SQL EXCEPTION: " + ex);
// Handle all type of database exceptions
switch(ex.Number)
{...}
}
catch (Exception ex)
{
Console.WriteLine("OTHER EXCEPTION: " + ex);
}
}
static void Main(string[] args)
{
Connection = new MySqlConnection(connectionString);
_timer = new System.Timers.Timer(3000);
_timer.Elapsed += new ElapsedEventHandler(_timer_Elapsed);
_timer.Enabled = true;
Console.ReadKey();
}
If the connection to MySql is lost, I got a general exception:
IOException : Unable to write data to the transport connection: An
established connection was aborted by the software in your host
machine.
I was expecting MySqlException to be fired but that was not the case.
Also, if the connection to MySql is restored, I still get the IOException instead of executing the query. Seems like, MySqlConnection object has not been updated and it doesn't care about new connection state.
What's the best way to handle connection lost exception?
How can I refresh MySqlConnection when connection is restored?
Note: that I can't instantiate a new MySqlConnection object for each new query, because the program I'm trying to change has a Singleton of type MySqlConnection which is initialized only once. I know that's a bad design but I don't want to change this design now. I just want to catch connection lost exception and try to refresh MySqlConnection to continue to work correctly.
If your MySqlConnection instance loses its connection to your MySQL server, you cannot expect that instances's connection to be restored automatically or otherwise.
You need to try to reconnect with a new instance of MySqlConnection. The one that has lost the connection is now in a terminal state and cannot be reused.
To do this, I suppose you could do something like this
...
catch (MySqlException ex)
{
if (/*ex is a connection drop */) {
Connection?.Dispose();
Connection = new MySqlConnection(...);
Connection.ConnectionString = /* your connection string */;
Connection.Open();
}
else {
throw;
}
}
You are correct that your design has a flaw. Whether or not your flaw is fatal is hard to tell without testing.
These Connection instances are not thread safe or in any way reentrant. If you use one in a timer handler or thread, you may only use it in that context. Otherwise, if it's already in use when your timer or thread is invoked, things will get dicey. If you're lucky you'll get an exception. If you're less lucky your MySQL server will receive gibberish from your client and detect it. If you're even less lucky your data will get scrambled up.
ADO.NET and the MySqlConnection object implement connection pooling. This matters because it makes opening connections, using them, and then closing them, a lot cheaper than you might have expected.
Sometimes MySQL drops connections that your programs have held open for long periods of time. This post may help if that is your problem.
How can I change the default Mysql connection timeout when connecting through python?
When you lost your connection by networks problems, the connection object does not change Status property so evaluate it before executting commands doesn't work.
However, the database property (connection.database) goes to empty string so you can evaluate it so can close the connection an restores it:
oConn is an instance of MySQLConnection (it works on odbcconnection)
[VB.NET]
If Not IsNothing(oConn) Then
If (oConn.Database.Equals(String.Empty)) Then oConn.Close()
End If
[C#]
If (Not IsNothing(oConn)){
If (oConn.Database.Equals(String.Empty)) oConn.Close();
}
I'm in the process of building a mobile companion app for a database system.
As the mobile app won't always have access to a data connection, I need to save any record changes to the local database on the tablet/phone when the internet is unavailable.
My initial thought was to simply use something like
public bool TestConn()
{
SqlConnection conn = new SqlConnection("some connection string")
bool result;
try
{
conn.Open();
conn.Close();
result = true;
}
catch
{
MessageBox.Show("Data Connection not found");
result = false;
}
return result;
}
then wrapping using an if statement to switch between the 2 databases ie. if true use remote, else use local
Is there a better way to handle this? I considered using a try-catch system where if the exception thrown is that it can't connect then it saves to the local database instead (assuming that can even be done). Is this even practical given the potential error codes that can be thrown?
I one of my c# application, i have written sql connection code as following
try
{
myConnection = new SqlConnection(m_resourceDB.GetResourceString(nSiteID, ApplicationID.XClaim,(short)nResID ) );
myConnection.open();
}
I want to handle unkown issue of sqlserver like database down, time out.
For this i though to introduce for loop 3 times with 3 minute sleep between loop and if at all problem is there then i will exit from loop
I don't know my though is right or not? I want some expert advice on this? Any example?
I would say simply: the code that talks to connections etc should not be doing a sleep/retry, unless that code is already asynchronous. If the top-level calling code wants to catch an exception and set up a timer (not a sleep) and retry, then fine - but what you want to avoid is things like:
var data = dal.GetInfo();
suddenly taking 3 minutes. You might get away with it if it is an async/callback, and you have clearly advertised that this method may take minutes to execute. But even that feels like a stretch. And if you are up at the application logic, why not just catch the exception the first time, tell the user, and let the user click the button again at some point in the future?
If you are running a service with no user interface, then by all means, keep on looping until things start working, but at least log the errors to the EventLog while you're at it, so that the server admin can figure out when and why things go wrong.
For a client application, I would no suggest that you make the user wait 9 minutes before telling them things are not working like they should. Try to connect, assess the error condition, and let the user know what is going wrong so that they can take it further.
If you are using the SqlException class you can check the Exception Class and decide based on that what is going wrong, for example:
switch (sqlEx.Class)
{
case 20:
//server not found
case 11:
//database not found
All the classes have the SQL Server message on them, it is a matter of testing the different conditions.
It really depends on how you want your application to behave.
If your database access is dealt with on the same thread as your UI then whilst you are attempting to connect to a database it will become unresponsive.
The default time period for a connection timeout is already pretty long and so running it in a for loop 3 times would triple that and leave you with frustrated users.
In my opinion unless your specifically attempting to hide connection issues from the user, it is by far better to report back that a connection attempt has failed and ask the user if they wish to retry. Then having a count on the number of times that you'll allow a reconnection attempt before informing the user that they can't continue or putting the application into an "out of service" state.
I want to handle unkown issue of sqlserver like database down, time out.
Try to surround connection operation with using statement to capture connection related problems .
using( sqlcon = new SqlConnection(constr))
{}
Use the Try/Catch Statement for capturing the exception:
try
{
con.Open();
try
{
//Execute Queries
// ....
}
catch
{
// command related or other exception
}
finally
{
con.Close();
}
}
catch
{
// connection error
}
To prevent Exception of such type check these:
Troubleshooting Timeout SqlExceptions
you can set the CommandTimeout to some value on a SqlCommand:
objCmd.CommandTimeout = 600
You can catch the SqlException.
SqlException.Class
Gets the severity level of the error returned from the .NET Framework Data Provider for SQL Server.
SqlException.Errors
Gets a collection of one or more SqlError objects that give detailed information about exceptions generated by the .NET Framework Data Provider for SQL Server.
SqlCommand cmd = new SqlCommand();
cmd.Connection = new SqlConnection("CONNECTION_STRING");
cmd.CommandText = "SELECT * FROM ....";
// cmd.CommandType = System.Data.CommandType.Text;
try
{
cmd.Connection.Open();
try
{
SqlDataReader reader = cmd.ExecuteReader();
// ....
}
finally
{
cmd.Connection.Close();
}
}
catch (SqlException ex)
{
// ex.Class contains the ErrorCode, depends on your dataprovider
foreach (SqlError error in ex.Errors)
{
// error.LineNumber
// error.Message
}
}
The best way would be to putt it in a try catch statement and display the error in a better format, If it fails for 1 time, trying it continue sly 3 times will not change anything untill and unless you dc and send request again, In a separate in separate packed as a new request.
use try this.
try
{
Executing code.
}
catch (Exception err)
{
Display["ErrorMsg"] = err.Message.ToString() + "|" + err.GetBaseException() + "|" + Request.Url.ToString();
}
Good Luck.